1
A COMPENDIUM OF HEXAPOD SYSTEMATICS
Niels Peder Kristensen
Entomology Department, Zoological Museum
Natural History Museum of Denmark, University of Copenhagen 2005
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INTRODUCTION: 'ENTOMOLOGY' AND ARTHROPOD PHYLOGENY
The Greek entomon and the Latin insectum both mean incised/sectioned and these words refer, of
course, to the segmentation of body and appendages. Linnaeus' 'Insecta' comprised all groups
currently known collectively as arthropods. In some academic traditions the term 'entomology' only
refers to insects (in a broad sense, i.e., = Hexapoda), but often the study of the other 'terrestrial'
arthropods, i.e., myriapods and arachnids, is - as here - considered part of 'entomology'. A detailed
treatment of the relationships between the principal arthropod lineages is outside the scope of the
present course. It necessarily requires consideration of the highly diverse (and probably nonmonophyletic) Crustacea, as well as of a suite of, partly bizarre, fossil groups, most of which were
(presumably primarily) aquatic. A brief outline of the main problems will, however, be presented at
the end of this introductory section.
THE ARTHROPODA
Generalities (RFB 518-5421 )
Segments and tagmata. Arguably a complement of paired excretory 'segmental organs'/'coxal
glands'/'nephridia' (with the opening associated with the limb base) should be added to outfit of a
generalized arthropod segment (RFB 518 and fig 16-1B); as noted RFB fig 16-15 (caption) these
have very restricted occurrence in hexapods and myriapods. Non-cuticular ('connective tissue')
endoskeletal formations may similarly be attributed to generalized arthropod segments; they
accommodate origins of extrinsic limb muscles and origins/insertions of body wall muscles. Such
formations become virtually eliminated in winged insects, where they are replaced by cuticular
endoskeletal formations that are ingrowths from the body wall.
The ground plan configuration of the paired segmental appendages has been much debated; in all
but the most anterior appendage it probably comprised a basal protopod(ite) bearing a telopod(ite)
and exopodite (recent comprehensive review by Boxhall, Biol. Rev. 79: 253-300, 2004). A subunit
in an appendage is referred to as a 'podomere2', or as a 'segment' (like the units in the trunk); it
typically moved by antagonistic muscles arising in the podomere proximad from it. The limb base is
typically moved by dorsal and ventral 'promotors' and 'remotors' originating, respectively, on the
tergal and sternal sclerotizations of the segment.
The patterns of 'tagmosis' (or tagmatization'), i.e., the integration of adjacent segments into
functional units, 'tagmata' are diagnostic of the principal arthropod lineages.
The caption for RFB fig 16-2, illustrating one pattern of arthropod tagmosis is misleading in saying "the abdomen
includes eight appendageless segments plus the telson". Behind the head and the three-segmented thorax with
locomotory legs one can actually count 10 legless (in dorsal view) abdominal segments plus an eleventh unit bearing
thread-like appendages (and tiny lobes mediad to the latter); this would correspond to the tagmosis pattern attributed to
the insect ground plan.
An arthropod body segment has by some morphologists been conceived as a structural unit, which
is so well-defined that one can meaningfully draw (on the basis of musculature, innervation etc.) a
“map” of the course of individual segment boundaries in those body regions (head and tail ends)
where the segment limits not are obvious; see below. Insertions of the dorsal and ventral
longitudinal muscles of the trunk are considered to demarcate the segmental boundaries; since these
insertions are typically situated on inflected transverse ridges (sulci) of the dorsal and ventral
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References in the style "RFB X" refer to p. X in the course textbook Ruppert, E.E., Fox, R.S. & Barnes, R. D. 2004:
Invertebrate Zoology, Thomson, Belmont.
2 The termination -mere (from Greek méros, part, portion) is also encountered in terms such as 'antennomeres'
(=subunits of the antenna), 'flagellomeres' (=subunits of the antennal flagellum of Insecta s.str.) and 'tarsomeres'
(=subunits of the tarsus of the leg):
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sclerotizations, the nearby 'intersegmental membranes' that provide mobility between these
sclerotizations are not exactly 'intersegmental' in a morphological sense.
It has been suggested that some hexapods have traces of thoracic ‘intersegments’ (understood as
incompletely developed segments) between the conventionally (and easily) recognized ones; this
remains controversial, however.
Body wall and its derivatives (RFB 521 ff). Invaginations from the outer integument, with
basically the same structure - a single layer of epithelial cells that secrete an overlaying cuticle form important components of the 'internal' anatomy of arthropods (fore and hind gut, outlets from
glands and gonads, endoskeletal formations, tracheal systems [in most terrestrial lineages]).
A couple of different chemical pathways may lead to the 'sclerotization' [sklerotisering] of the
cuticle, i.e., to the formation of the hard exocuticle through formation of cross-links between cuticle
proteins. Sclerotization is not necessarily accompanied by a darkening of the cuticle although that is
most often the case. Note: the classical expression "strongly chitinized" for particularly hard and/or
dark cuticle is in any case misleading, in as much as these properties are in no way related to the
amount of chitin present.
A technical note: Unlike other tissues the cuticle is not dissolved upon immersion (and even boiling for a moderate
length of time) in KOH. KOH maceration is therefore widely used for making cleared preparations of, e.g., genitalia
segments or heads with mouthparts for taxonomic or morphological study. Unsclerotized cuticle may be stained with
several histological stains, whereas exocuticle is refractory to stain, presumably because of the dense 'packing' of cuticle
material. Endocuticle below the exocuticle may show staining properties different from that of procuticle in adjacent
membranous regions; this is the explanation why staining may often lead to improved differentiation between 'sclerites'
and 'membranes'.
Small protuberances of the exoskeleton come in many forms and are often taxonomically
important; a 1979 review article by Richards & Richards (Int. J. Insect. Morphol. Embryol. 8: 143157) remains a most useful reference. Of special note are the sensilla (='exoreceptors' except for
photoreceptors, RFB 532ff, including setae RFB 523 and figs 13-5B, 16-4) which in what may be
considered the basic type are formed after two consecutive divisions of an epidermal cell. Of the
four cells in the resulting cell 'tetrad' the outermost is the 'tormogen cell' secreting the sensillum
socket membrane; it envelops the 'trichogen cell' which forms the variably shaped external cuticular
part of the sensillum and a sensory neuron, while the fourth is an enveloping glia cell (called
'thecogen' in RBF fig 13-5B) surrounding the neuron; in chemoreceptive sensilla additional cell
divisions generate multiple sensory neurons (RFB fig 16-12A). Note the mention (RFB 533) of a
"derived cilium" pertaining to sensillum organisation; it is located in the apical dendrite of the
sensory neuron. Not all setae/'hairs' are innervated; in this case only one of the daughter cells
resulting from the initial epidermal cell division divides again, and the trichogen cell may
eventually be eliminated altogether.
In addition to the process types listed, the so-called 'acanthae' should be mentioned; these are
(sometimes quite large) cuticular processes formed by just a single epidermal cell; hence they are
devoid of a socket.
The most common epidermal (or 'tegumentary' , the term used by RFB 523) glands are derived
from epidermal cells dividing in a manner reminiscent of the formation of sensilla; interestingly a
cilium-like structure is also formed by one of the cells during gland development, but it is soon
becomes eliminated, hence it is not present in the definitive functional gland.
The outlet of the most common gland type is surrounded by one or more tenuous epidermal cells, not shown in RFB
fig 16-4.
The unlabelled rounded cells interspersed between the columnar epidermal cells in RFB fig 16-4
are called oenocytes; they also originate through division of ordinary epidermal cells, and
frequently become much larger than the latter. They may remain in contact with the epidermis as
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shown in RFB fig 16-4, but at least in neopteran insects they may migrate into the body cavity; they
synthesize wax which is eventually exported to the epicuticle where it is important for its
waterproofing properties. Oenocytes are widespread among winged insects, but it is uncertain
where they first evolved within the hexapods.
Arthropod monophyly. There is currently near-consensus that arthropods as here delimited (i.e.,
excluding Onychophora) are indeed a 'natural' (i.e., monophyletic) group, but arthropod polyphyly
theories have been in vogue in parts of the biologists' community for several decades, prompted
particularly by a seminal 1958 review article by Tiegs & Manton (Biol. Rev. 33: 255-337) and
subsequent Manton writings (summarized in The Arthropoda. Habits, functional morphology, and
evolution. Clarendon Press, Oxford. 1977); the most recent principal advocate is Fryer (extensive
account in Biol. J. Linn. Soc. 58: 1-55, 1996). Putatively derived character states that can be
attributed to the ground plan of the Arthropoda (i.e., arthropod 'autapomorphies', see section 3) are
listed RFB 539.
Arthropod ‘deep’ phylogeny. The 'conservative' phylogeny of extant taxa is
Chelicerata+(Crustacea+(Myriapoda+Hexapoda3)). The characters listed RFB fig.16-15, caption, in
support of the monophyly of the 'Mandibulata' (=Crustacea+(Myriapoda+Hexapoda)) are partly
debatable as apomorphies at the arthropod level. Of particular interest is an extraordinary similarity
of the ommatidia of the compound eye in the groundplans of the Crustacea and Hexapoda;
compound eyes in myriapods (present only in scutigeromorph chilopods) can alternatively be
interpreted as being secondarily modified from the ancestral Crustacea-Hexapod-type or a
forerunner of it (Paulus, J. zool. Syst. Evol. Research 38: 189-208, 2000).
Few zoologists would contest the notion that hexapods descended from a largely homonomously
segmented arthropod which would be phenetically classified as 'a myriapod', and at least three
names have been in frequent use for the Myriapoda+Hexapoda assemblage: Atelocerata, Tracheata
and Antennata. The first-mentioned (and arguably the preferable one) refers to the absence, in these
animals, of distinct segmental limbs on the head segment behind the antennal segment (and the
counterpart of which in the Crustacea bears the 2nd antennae); this condition is indeed a potentially
true synapomorphy of the two groups. ‘Tracheata’ alludes to the presence of tracheae in myriapods
and hexapods, but it remains very debatable whether tracheae actually were present in their last
common ancestor. The tracheae of scutigeromorph chilopods have with certainty been
independently evolved – and tracheal systems have been independently evolved repeatedly in
arachnids also.
‘Antennata’ is a complete misnomer, in as much as also Crustacea have (even two pairs of) antennae, and so had some
fossil arthropods (e.g. the well known trilobites) that are not closely related to myriapods and hexapods; in contrast, the
more rarely used 'Monantennata' is indeed meaningful.
To the potential synapomorphies of myriapods and hexapods listed by RFB could be added the
presence of anterior tentorial arms (see subsequent discussion of hexapod head structure) and the
absence of levator muscles of the pretarsal claws (the claw depressor - which originates in the tibia,
never in the tarsus! - works against hydrostatic pressure and/or cuticle elasticity; this condition is
paralleled in subordinate arachnids) and perhaps the presence of fat body. The significance of
Malpighian tubules is debatable; the latter are developed from the ectodermal proctodaeum rather
than from the entodermal midgut as they reportedly are in arachnids, but both modes are recorded
3
The name 'Hexapoda' is here used for the assemblage comprising the primarily wingless Collembola, Protura,
Diplura (s. l.), Archaeognatha, Zygentoma and the winged insects (Pterygota); the name 'Insecta' is restricted to the
unquestionably monophyletic entity Archaeognatha+Zygentoma+Pterygota. In some (notably German) texts one will
find the last-mentioned entity referred to as 'Ectogantha' while 'Insecta' is used in the same sense as 'Hexapoda' here.
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within the insects (and ‘entoderm’ is a somewhat problematical concept in arthropods anyway).
From the 1990s the above-mentioned phylogenetic model has been challenged by evidence
(primarily molecular, but also from neuroanatomy a.o.) for a monophyletic 'Pancrustacea' =
Crustacea+Hexapoda. Essential background information, and references, on these issues are given
in two volumes edited, respectively, by Fortey, R.A. & Thomas, R.H. (Arthropod Relationships.
Chapman & Hall, London ,1997) and Deuve, T. (Origin of Hexapods. Ann. Soc. ent. France (N.S.) 27
(1/2), 2001). The monophyletic Pancrustacea emerges in different scenarios of arthropod evolution.
Crustacea and Hexapoda may be sister groups, or the latter subordinate in the former. A recent
study on brain stucture led to the proposal of a pancrustacean subgroup comprising
Remipedia+Malacostraca+Hexapoda (Fanenbruck et al., Proc. Natl. Acad. Sci. USA, 101: 38683873, 2004; also Fahrbach ibid.: 3723-3724).
An otherwise conventional topology: Chelicerata+(Crustacea+(Myriapoda+Hexapoda)) is
retrieved in a major 'total evidence4’ study (Giribet, Edgecombe & Wheeler, Nature 413: 157-161,
2001); note, though, that in the single tree obtained with the preferred settings, the immediate sister
group of Crustacea is a bizarre assemblage comprising the primarily apterous hexapod family
Japygidae (Diplura), the crustacean Nebalia - and Drosophila! It is sobering, that in the same issue
of Nature (see also Blaxter, Nature 413: 121-122, 2001) support for a
(Myriapoda+Chelicerata)+(Crustacea+Hexapoda) phylogeny was published by Hwang et al.
(Nature 413: 154-157, 2001), based on mitochondrial protein sequences.
Yet another model retained the conventional monophyletic Myriapoda+Hexapoda monophyletic,
but had it subordinate in Crustacea (Moure & Christoffersen, J. comp. Biol. 1: 95-113, 1996).
The Lower Devonian fossil Devonohexapodus bocksbergensis, described in early 2003 (Haas,
Waloszek & Hertenberger, Org. Divers. Evol. 3: 39-54), is believed by its authors to belong to the
hexapod stem lineage. Devonohexapodus has a single pair of antennae and its postcephalic trunk
comprises a three-segmented thorax with long locomotory limbs, followed by an abdomen of 35+
homonomous segments with small (but still segmented) leglets; the leglets of the three hindmost
limb-bearing segments are modified, backwards pointing. Devonohexapodus was in all probability
marine - hence the authors who subscribe to monophyly of Atelocerata conclude that the stem
lineage of this asssemblage was marine as well.
Hexapod monophyly long remained uncontested, but molecular studies published in 2003 and
2004 have suggested two different scenarios of hexapod paraphyly (see subsequent treatment of
basal hexapod phylogeny).
It is abundantly clear from the above that the problems about the interrelationships of the
principal arthropod lineages are far from solved by the beginning of the 21st century!
THE HEXAPODA
Information sources
Comprehensive accounts. Two series of major reference works should be known to all workers
dealing with in systematic/general entomology, namely
Grassé, P.P. (ed). Traité de ZoologieVIII-X (1949-79) Insectes; vol. VIII in many, vol. X in two
"fascicules". The systematic accounts are in IX (1949) & X (1951) hence, of course, now
considerably outdated.
Beier, M., subsequently Fischer, M., currently Beutel, R. & Kristensen, N.P. (eds) Handbuch der
Zoologie/Handbook of Zoology. Arthropoda, Insecta, 2nd edn since 1968; still in course of
4
The term ‘total evidence’ is current jargon for a phylogenetic study that considers both molecular and morphological
evidence simultaneously.
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publication. A few of the smaller hexapod 'orders' (Diplura, Zygentoma, Mantophasmatodea,
Siphonaptera) are not yet treated, and of the major endopterygote 'orders' only volumes dealing with
the Diptera, Lepidoptera and Hymenoptera-'Symphyta' have appeared. The first of three planned
volumes on Coleoptera is nearing completion. While the series was initially published in German,
recent issues are (and all future ones will be) in English.
The individual chapters/issues in the Traité as well as in the Handbuch/Handbook series are of
very unequal quality.
The most recent, somewhat detailed, systematic handbook account of the arthropods as a whole is
Parker, S. (ed.) Synopsis and Classification of Living Organisms, vol.2, New York etc.,
McGrawHill, 1982. Arachnida pp. 72-169, Insecta pp. 326-680, Myriapoda pp. 681-726. A multiauthor treatment with special emphasis on family-group taxa. Unfortunately 'under-illustrated'. The
entognathan hexapods have been inadvertently omitted in this work!
Three books by R. Matsuda on the tagmata of the hexapod body:
Morphology and evolution of the insect head. Mem. amer. ent. Inst. 4, 334 pp., 1965,
Morphology and evolution of the insect thorax. Mem. ent. Soc. Can., 76, 431 pp., 1970,
Morphology and evolution of the insect abdomen. Oxford, Pergamon Press, 543 pp., 1976,
are immensely useful references with (for their time) near-exhaustive bibliographies. However,
Matsuda's own interpretations, and his original contributions, are partly problematical. The head
and thorax books are essentially about adult skeletomuscular anatomy. In contrast, the abdomen
book has no musculature account, but considers morphogenesis in some detail; it also treats the
internal genitalia. As far as the head and abdomen (i.e., abdominal skeletomuscular structure) are
concerned, the accounts by (Denis &) Bitsch in the Traité de Zoologie are preferable. The head is in
VIII(I), 1973, the abdomen in VIII(II), 1979 (where one also finds a French version of Matsuda's
thorax account; a little condensed, but also a little updated).
The morphology (including ultrastructure) of internal organs is largely treated in the physiological
literature. A most comprehensive (13-volume) account of insect physiology was published in 1985:
G.A. Kerkut & L.J. Gilbert (eds) Comprehensive Insect Physiology, Biochemistry & Pharmacology,
Oxford, Pergamon Press. The most modern reference on organs other than the skeletomuscular
system is a three-volume treatise edited by Harrison, F. W. & Locke, M. 1998: Microscopical
Anatomy of the Invertebrates, 11A-C, Insecta A-C. New York, Wiley. Unfortunately, treatments of
some organ types/systems (chemoreceptors, simple eyes, testes, etc.) are entirely lacking.
Condensed accounts. CSRIO (ed) The Insects of Australia 1-2, 1137 pp. Melbourne University
Press 1991, and Richards, O.W. & Davis, R.G. (eds) Imms' General Textbook of Entomology 1-2,
1354 pp, Chapman & Hall, 1977 have long been considered the leading compact references on
hexapod anatomy/physiology/systematics. The latter (evidently somewhat outdated) has a much
more detailed general part, while the systematic treatment is more authoritative and up-to-date in
the latter (which is multi-authored); of course it is a limitation that non-Australian taxa below
'ordinal' level are omitted. The recently published 'revised Insect Kaestner', i.e., Dathe, H. (ed)
Lehrbuch der Speziellen Zoologie. Begründet von A.Kaestner, 2 Auflage, Band I: Wirbellose Tiere,
5. Teil: Insecta. Spektrum 2003, effectively replaces vol. 2 (systematics) of 'Imms', though
references are somewhat sparser.
Rasnitsyn, A. P. & Quicke, D. L. J. (eds) History of Insects, Kluwer Academic Publ. 2002 presents
the principal insect lineages with emphasis on their fossil record; the systematic approach is noncladistic. Grimaldi, D. & Engel, M. Evolution of the Insects (Cambridge University Press,
publication expected spring 2005) will present an extensive (and exquisitely illustrated) account of
insect evolution. Like the Rasnitsyn & Quicke volume it is an integrated account of both fossil and
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extant taxa, but it its coverage of phylogenetically informative morphological characters is more
detailed, and systematics is treated from a modern, cladistic perspective.
F. Stehr (ed.). Immature Insects. 1-2, Kendall/Hunt1987-1991 is a most useful treatment of
(external) morphology and taxonomic characters of insect nymphs and -larvae. Based on the North
American fauna, but widely applicable.
RFB 751 lists a number of more succinct single-volume entomology texs; to these may be added
Gullan, P. & Cranston, P. The Insects. An Outline of Entomology, Blackwell, 3rd edn 2004) and
Dettner, K. & Peters, W. (eds) Lehrbuch der Entomologie, G. Fischer1999; a revised 3rd edn of
Gillot, C. Entomology, New York, Plenum is forthcoming in 2005. Chapman, R. F. The Insects.
Structure and Function, Cambridge, Cambridge University Press (4th edn 1998) is a particularly
information-rich, compact account of insect physiology; morphology is treated in less detail.
There are two recently published entomological 'encyclopedia': Capinera, J. L.(ed) Encyclopedia
of Entomology (3 vols), Kluwer Academic Publ 2004 , and Cardé, R. & Resh, V. H. (eds)
Encyclopedia of Insects, Academic Press 2003.
Reviews. Review articles in Annual Review of Entomology are important introductions to the
literature on many topics. The same is true of many articles in the more recently initiated Annual
Review of Ecology & Systematics series.
Tools for identification of Danish/N.European hexapods. M. Chinery’s Collins Guide to the
Insects of Britain and Western Europe appeared in a Danish edition (translated/revised by Henrik
Enghoff) Vesteuropas Insekter Gad 1987. (There are later reprints, but it is now out of print; a new
edition of the English original is forthcoming in 2005). It treats (with mostly excellent illustrations)
a sizable selection of European insects and, more succinctly, other terrestrial arthropods.
Undoubtedly the most useful introduction to the diversity of our hexapod fauna. Another, similarly
recommendable book in the same category is Douwes, P., Hall, R., Hansson, C. & Sandhall, Å:
Insekter. En fälthandbok, Interpublishing, Stockholm 1997. It is less richly (but still richly – with
good colour photographs) illustrated than the Chinery book, but is more technical, with
identification keys to superfamily/family level.
The principal series of identification manuals of relevance are Danmarks Fauna (publication of
hexapod volumes almost ceased), Svensk Insektfauna (publication ceased), Fauna Entomologica
Scandinavica (an English-language ‘replacement’ for the two preceding series), Danmarks Dyreliv,
Handbooks for the Identification of British Insects and Tierwelt Deutschlands. A national tool for
finding identification literature, is Lomholdt, O., Nielsen, P. & Schnack, K. (ed.) 1984:
Entomologisk Litteratur - en hjælp til studiet af den danske insektfauna. Ent.Meddr 51(1-2), 85 pp.
A few newer identification manuals are mentioned in the present text. But otherwise reference can
be made to the immensely useful bibliographical tool by P. Barnard (ed.): Identifying British Insects
and Arachnids. An Annotated Bibliography, Cambridge University Press 1999. An important
modern guide to identification of freshwater insects is a two-volume manual edited by A.Nilsson:
Aquatic Insects of North Europe. A Taxonomic Handbook. 1-2, Apollo Books, 1996-1997.
There are still large sectors of the NW European hexapod fauna for which no useful identification
manuals are available, notably in the Diptera and parasitic Hymenoptera. Hopefully an ambitious
Swedish ‘Nationalnyckel’- initiative will lead to this situation being remedied within the next
couple of decades.
Internet information. The entomology websites listed RFB 751 are but a small fraction of those in
existence. Websites may be centred on taxa, organ systems etc.; they can be found using standard
search machines.
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While the internet holds great promise as a medium for whole-organism science, it cannot be overemphasized that the bulk of the existing information on hexapod systematics and morphology is
presently available only in printed form. It similarly important to note that the greater part of the
pertinent literature on these topics was published before the period covered by the principal
bibliographic databases available in electronically searchable form: BIOSIS previews from 1969,
and (the more complete) Zoological Record from 1972. Also, one must be aware that much (indeed
most) of the fundamental morphological work on hexapods is published in languages other than
English (primarily German and French).
Hexapod body design: structure and function (RFB 517-539; 724-740)
As already mentioned, the time-honoured taxon here called Hexapoda comprises the Collembola,
Protura, Diplura (s. l.) and Insecta = Archaeognatha+Zygentoma+Pterygota. The monophyly of this
arthropod assemblage has been inferred primarily from the unique type af tagmosis shared by its
members; it is the one illustrated in RFB fig 16-2 (note the reservation about the caption text on p. 2
above), see also Fig 11A here. Of crucial significance is the differentiation of the postcephalic
thorax, comprising three segments with relatively large locomotory limbs; in contrast limbs suitable
for walking are absent from the abdomen.
Other potential hexapod ground plan autapomorphies are mentioned below, as is conflicting
evidence for hexapod non-monophyly.
A summary cladogram of principal hexapod lineages such as Fig 1. here can serve as a basis for
the following supplements to the summary general account of hexapod structure and function RFB
724-744. Many characteristics of higher insects were not evolved in the hexapod ground plan evidently the evolution of wings in the stem lineage of the Pterygota was associated with a major
innovation of general body design.
The head and its appendages (RFB 520, 724-726, 727-730; figs 16-3, 21-1A,B; 21-3-7; Figs 2-3
here). The segments composing the hexapod head tagma are fused into a solid capsule. The RFB fig
16-3 representation of the head of "Tracheata" (and hence hexapod) as comprising an eye-bearing
acron (= ocular or protocerebral segment) plus 5 following segments (antennal or deutocerebral,
intercalary5 or tritocerebral, mandibular, maxillary and labial segments) complies with the
probably most widely accepted interpretation, but it is not the only one. The RFB 724 account of
the hexapod head as being composed of "an unknown number" of segments arguably remains
correct: available evidence supports partly incompatible models.
The Drosophila-based model (outlined on RFB 724) which recognizes a labral segment in front of the ocular segment,
and distinguishes between the latter and the anteriormost "archicerebrum" component is one of the alternatives, while
according to another (also based on Drosophila developmental genetics) the labral segment follows behind the ocular
segment The labrum otherwise has long been widely considered to belong, at least largely, to the tritocerebral segment,
as indicated by its innervation (RFB fig 21-7), and indeed some recent gene-expression work on hexapods other than
Drosophila has brought new support to previous proposals that it represents fused limbs of this segment. But if this is
5
The figure caption statement "0= lost segment" is misleading, in as much as what is "lost" is just the segmental
appendage pair (at least as limb-like formations), while the segmental neuromere, the tritocerebrum, is distinct. As for
putative limbs of the segment, see the comments on labrum and superlinguae.
Incidentally, the conventional homologization of the chelicere-bearing segment in Chelicerata with this
hexapod/myriapod intercalary segment, and the crustacean second-antenna-segment which is shown in the same figure
has been challenged by recent gene-expression and neuroanatomical work that supports homology of the chelicere and
the first antenna in mandibulate arthropods (see e.g., Mittmann & Scholtz, Development Genes and Evolution 213: 917, 2003).
9
true, the hexapod labrum cannot (at least in its entirety) be homologous with the labrum in Crustacea, in which the
tritocerebral-segment limbs are the 2nd antennae.
Yet another theory of hexapod head segmentation is shown in Fig 2A here. It recognizes (primarily for
neuroanatomical reasons) the presence of a “tetrocerebral” segment located between the tritocerebral and mandibular
segments.
The term clypeus (RFB figs 21-1A, 21-7) applies to the part of the head capsule, which
accommodates the origins of those sucking pump dilator muscles that insert outside the loop formed
by the connectives from the frontal ganglion to the tritocerebrum (Fig 2C). In Dicondylia the
clypeus can sometimes be externally delimited from the upper facial region, the frons by an
epistomal sulcus on the head capsule, but a sulcus running between the anterior tentorial pits will
sometimes prove to be transclypeal.
Endoskeletal formations in the hexapod head come in two forms: the tentorium formed by rodlike/lamellar invaginations from the head capsule (hence cuticle-lined) and genuine connective
tissue formations. In the hexapod ground plan the latter are well developed and serve the origin of
several muscles inserting on the antennae, mouthparts (Fig. 2B), food tract etc. Within the basal
Insecta they become step-wise replaced by the cuticular tentorium (which is atypically or not at all
developed in other hexapods), and in the winged insects only the latter remains. When fully
developed (Fig 2D) the tentorium comprises two anterior tentorial arms invaginated from the
head capsule just in front of/above the mandibular base, and two posterior tentorial arms
invaginated from the lower posterior surface of the head capsule, close to its posterior opening
('foramen magnum'); the invagination sites, 'tentorial pits' are extenally identifiable as pits or slits.
Moreover the anterior and posterior arms fuse into a solid framework, and the posterior arms fuse to
form a transverse bridge ('corpotentorium'). Dorsal tentorial arms are outgrowths on the anterior
arms; they accommodate the origin of antennal muscles.
Hexapod antennae [følehorn] similarly come in two forms: in those of Collembola and Diplura
each individual antennomere is movable by muscles arising in the preceding one, as in a generalized
arthropod limb (Fig. 3B). Those of the Insecta (Fig. 3A) only have muscles between the basal
segment, scapus, and the base of the following, pedicellus. The entire antenna beyond the
pedicellus is termed flagellum, and its individual segments ('flagellomeres') therefore are movable
relative to each other only through interplay between blood pressure and cuticle elasticity. The
prominent group of mechanoreceptive chordotonal organs characteristic of the insect pedicellus is
called Johnston's organ (Fig 3C).
The hexapod mandible [kindbakke] is considered to represent the basal limb portion; compared
with the crustacean mandible illustrated RFB fig 19-2 the conspicuous difference is its lack (shared
with/paralleled by myriapod mandibles, and also in certain subordinate crustacean lineages) of a
telopodite, 'palp'. Also, expression of the Distalless (Dll) gene, marker for telopods, is completely
absent in examined developing hexapod mandibles; it is transiently expressed in some myriapods.
The articulation between the head capsule and the mandible is of considerable interest in the
question of the first splitting event identifiable within the Insecta s.str. A ‘new’ anterior mandibular
articulation has long been considered a synapomorphy of the Zygentoma [sølvkræ-gruppen] and the
Pterygota, cp. the name Dicondylia. However, in both Zygentoma and Ephemeroptera (mayfly
[døgnflue]) nymphs there are actually two anterior mandibular articulations (with the clypeus and
the base of the anterior tentorial arm, respectively), but the connection remains fairly loose. A close
contact between an area on the anterior mandibular surface and the head capsule in the anterior
tentorial pit region actually occurs also in Archaeognatha and some entognathans, though one can
here hardly talk about a genuine articulation; the connection permits a rolling of this slender
mandible around an oblique-vertical axis (Figs 3D, 11B-D). This close contact could be
plesiomorphic at the hexapod level. It has been suggested (Koch, Ann. Soc. ent. France (N.S.) 27
(1/2): 129-174, 2001) that the anterior mandibular articulation is secondarily reduced in
10
Archaeognatha, as indicated by the presence here of a complement of extrinsic mandibular muscle
bundles that is smaller than that ascribed to the hexapod ground plan. Bitsch (Ann. ent. Soc. France
(NS) 37: 305-321, 2000) argues that the shape and the anterior cranial connection of the
zygentoman/ephemeropteran mandible is indeed an intermediate stage between the mono- and
dicondylous types. In any case a truly firm dicondylous articulation between the head capsule and
the mandible (whereby the mandibular movement is restricted to a transverse swing around the axis
between the two articulations, making for a strong bite) is a putative synapomorphy of the Odonata
(dragonflies [guldsmede]) and Neoptera; it is the type illustrated in Fig 2A here. In the posterior
(ancestral) articulation a mandibular condylus [ledtap] fits into a cranial ginglymus [ledgrube]; in
the anterior articulation (the neoformation things are reversed. Besides large cranial ab- and
(particularly large) adductor muscles the mandible primitively has also a ventral adductor that
originates from the tentorium and, in the most basal taxa (cp. Fig 2B here) also on the connectivetissue endoskeleton; this ventral adductor is reduced or completely lost in many advanced insects.
Generalized hexapod maxillae and labium are illustrated Fig. 3E-F here; familiarity with the
names of the constituent elements of these appendages is required for easy access to the enormous
body of writings on insect mouthparts in a functional-morphological and/or taxonomic context. The
maxilla comprises the basal cardo, followed by the stipes which bears the maxillary palp and two
endite lobes, the outer galea and the inner lacinia. The labium comprises a basal postlabium
(sometimes transversely divided into a basal submentum and a distal mentum) and a distal, often
bilobed prelabium6 whose appendages, reminiscent of those of the maxillary stipes are the labial
palp and two endites, the inner glossa and the outer paraglossa.
The tounge-like hypopharynx is morphologically mostly composed from the ventral regions of
the mandibular and maxillary segments; it forms the floor of the preoral cavity which is enclosed
beween the mouthparts. In very generalized hexapods it bears a pair basal lobes, the ‘superlinguae’
(Fig. 11E), which by some morphologists have been considered vestigial appendages of the
‘tetrocerebral’ segment (see above).
Thorax [bryst] (RFB 726-727. The RFB diagram fig 21-1D depicts what is probably a widespread
concept of a generalized 'pre-wing' thoracic segment7. It well illustrates the discordance between
functional and morphological segment borders (the latter indicated by dashed vertical lines). Note
that the pleural sclerotizations comprise two crescent-like plates (they were presumably somewhat
narrower in the hexapod ground plan) one above the other, and that the ventral intersegmental
sclerotizations are discrete (in the putatively generalized state; in subordinate lineages they may
become synscleritous with adjacent sterna). They normally bear a median spine-like apodeme, and
are therefore referred to as spinasterna.
The head is somewhat, indeed in some lineages extremely, mobile relative to the thoracic trunk;
this mobility is due to the presence of an ample membranous cervical region (or just 'cervix')
between the head capsule and the principal prothoracic sclerites. Winged insects have one or more
cervical sclerites (or 'laterocervicalia') in the cervical membrane; they are believed to represent
elements detached from the propleural trunk sclerotization, and they may form articulations
6
The pre- and postlabium are sometimes alternatively referred to as pre- and postmentum, respectively.
Terminology notes: 'tergite' as used in the RFB figure is strictly synonymous with 'tergum used here; sternite/sternum
is a similar case. Some would claim that the -ite suffix should denote something that is a subsection/part of the tergum
or sternum. If one uses the term 'pleuron' for the entire lateral body wall between tergum and sternum, then the RFB use
of pleurite for the sclerotizations in this region is in accordance with the afore-mentioned principle. Alternatively one
may find the term pleuron used for all pleural sclerotizations together.
The term notum is often used as a synonym for a thoracic tergum, particularly when referring to the tergal plate of an
individual thoracic segment: pronotum, mesonotum and metanotum.
7
11
between the latter and the head (and with each other, when there is more than just one on each side).
Morphologically the cervical region largely pertains to the prothorax, but evidence from
development and innervation indicate some participation of labial segment components.
Like the head the thorax has an elaborate endoskeleton which in the apterygote hexapods is
mainly formed by non-cuticular elements, but which in pterygotes is formed by apodemes
invaginated from the sterna, pleura and terga.
The modifications of the thorax treated associated with wing evolution is treated in the
'PTERYGOTA' section below.
The thoracic limbs of hexapods are usually ascribed the six podomeres coxa, trochanter, femur,
tibia, tarsus, and (the claw-bearing) pretarsus labelled in RFB fig 21-1E; the illustrated
subdivision of the tarsus into a numbers of tarsomeres (which are not individually musculated)
characterizes the Insecta s.str., not the hexapod ground plan. Hexapod limbs are also usually
described as 'uniramous'; note, however, the small stylus near midlength of the coxa in
Archaeognatha (Fig 11F.). In Palaeozoic fossil pterygotes Kukalová-Peck (review chapter on
fossils, pp. 141-179 in CSRIO [ed] The Insects of Australia 1, Melbourne University Press 1991)
has identified what appears to be segmented appendages arising from the joint membranes between
a number of the basal limb segments (inclusive of a 'subcoxa' located proximad from the coxa and
apparently homologous with the pleuron in modern pterygotes), and she interprets the wing as a
corresponding 'exite' on an even more proximal limb segment, the 'epicoxa', which like the subcoxa
has become incorporated in the lateral body wall. The concept of the pleural sclerites being derived
from a proximal limb segment has actually long been widely accepted.
A 'prefemur' and a 'patella' have similarly been claimed to be identifiable in these old fossils, but there is no general
agreement among 'neo-entomologists' that such segments must be ascribed to the ground plan of the hexapod limb. The
same is true for the recognition of the most proximal tarsomere ('basitarsus') as something basically different from the
following. The trochantin (a small sclerite basad from the coxa, shown but not labelled in RFB fig. 21-1E) is
presumably a piece split off from the coxal margin.
The question whether the pretarsal claws were paired or unpaired in the hexapod ground plan are
inextricably linked to the question of the phylogenetic position of the Diplura - and ultimately to the
question of hexapod monophyly; see below. Some accessory pretarsal processes (including the
'arolium' mentioned RFB 726, a sometimes very prominent, softwalled lobe below the claws)
apparently only evolved within the Pterygota.
Abdomen [bagkrop] (RFB 726, 736-738, figs 21-1F, 11B, 12B-C). The hexapod abdomen is
generally believed to be primitively twelve-segmented (eleven genuine metameres plus the telson),
so an ad hoc explanation (e.g. arrested anamorphosis) is needed in the case of the Collembola,
which have only six segments, and the Diplura (in which a segment XI8 may never be identifiable).
The gonopore is consistently located near the hind end of the abdomen. In the Insecta the female
gonopore is apparently primarily just behind sternum VII, but in various subordinate lineages it
becomes displaced to segment VIII or IX; the male gonopore is located in the IX-X boundary
region (the RFB statements on gonopore positions are oversimplified). The anus is located on the
terminal segment.
The limbs on abdominal segments I-IX, when retained, are much smaller and weaker than those
of the thorax and at least in extant hexapods they contribute at most minimally to locomotion9. RFB
says that "some Entognatha10 have small sensory styli that may be derived from appendages", but
8
The style of denoting abdominal segments by Roman numerals used here is widespread, but not universal. Many
authors would use Arab numerals for abdominal segments and Roman for the three thoracic segments.
9 The highly specialized collembolan furca on IV is an obvious exception.
10 As will be discussed below, it remains uncertain whether the assemblage of entognathous hexapods is a
12
the appendicular nature of these styli (present in Diplura and, in more regressed state, Protura) is
apparently generally accepted. Moreover, styli are particularly well developed (though never
segmented) on a variable number of abdominal segments in extant apterygote Insecta. Judged from
conditions here a typical mid-abdominal segment in ancestral insects would have comprised an
anterior sternal plate, which on the posterior margin bears a two-segmented appendage comprising a
large coxopodite and a slender stylus. Mediad from the stylus the coxopodite bears one or two
membranous eversible (or exsertile, or protrusible) vesicles (also called 'coxal sacs' [coxalsække])
which like the stylus receive muscles arising in the coxopodite; the epidermis of these vesicles can
actively absorb moisture from water film on the substrate.
Some Palaeozoic apterygote Insecta (Cercopodata, a group with debatable status) apparently had
the abdominal styli segmented and claw-bearing, hence overall similar to the distal parts of the
thoracic legs, although smaller (Fig 8 A). Appendages are absent on the pregenital segments of
extant pterygotes. It is noteworthy, though, that reduced, but still segmented limbs have been
identified here in (both nymphs and adults of) pterygotes belonging to extinct non-neopteran
groups, see Fig 4D.
Segment X was probably always devoid of limbs in the Insecta (though limb rudiments X may
participate in the formation of the phallic apparatus, see below). The dorsal sclerite of segment XI is
referred to as epiproct while the ventral sclerotization is divided into paired plates called
paraprocts ((RFB fig 21-11B, 12B-C).
The limbs of segment XI are termed cerci. In extant apterygote inscts and some pterygotes these
are prominent, thread-like and multiannulated appendages; a similar type occurs in DipluraCampodeidae, and it has long been attributed to the hexapod ground plan. However, recent
reassessments of the affinities of the Diplura raise doubts about this (see below), and also, in the
afore-mentioned Palaeozoic Cercopodata even the cerci have been interpreted as having been short
and having paired apical claws (Fig 8 A). Another Palaeozoic taxon, Monura, seems (most probably
secondarily) devoid of cerci (Bitsch & Nel Ann. Soc. ent. Fr (NS) 35: 17-29, 1999). In most
neopteran pterygotes the cerci are markedly shortened (RFB 21-11B, 12B) or lost.
Abdominal specializations characterising specific hexapod lineages, and those associated with
reproduction, are dealt with below.
Alimentary canal, 'gut' [tarmkanal] and associated structures RFB 530, 729-732, 735, figs 169, 21-7-9. A 'crop' is developed independently on more occasions; it is not a hexapod ground plan
trait. An elaborate gizzard also has a scattered occurrence in hexapods.
It is strongly developed in such basal hexapod lineages as 'core Zygentoma' (not Tricholepidion), Odonata and some
'lower neopterns'dragonfly, and its resemblance to that of some malacostracan Crustacea is intriguing. But there are no
similar formations in entognathans, Archaeognatha and Ephemeroptera.
In the context of the discussion of labial glands RFB 528, 730 mention "labial nephridia" only
from entognathans, but these formations also occur in apterygote insects (including Zygentoma), as
correctly stated RFB 735.
Odinary midgut epithelium cells have the apical surface (i.e., that facing the lumen) produced into
long close-set microvilli, while there are extensive infoldings of the basal surface; both features
testify to intense transport acticity. Midgut caeca [blindsække] are absent in entognathans but may
be an insect ground plan trait; they are quite variably developed. The entire gut is enveloped in a
muscular coat of more or less regular longitudinal and circular fibres. In some gut regions these
may only form a weak, open network while in others the 'muscularis' may be strongly developed (as
in 'gizzards').
monophylum; if it is not, use of a taxon name 'Entognatha' is unjustified.
13
It remains uncertain whether the rudimentary Malpighian tubules in entognathans are secondarily
reduced. While RFB 735 say these tubes are "poorly developed... in apterygotes" they are quite well
developed in the apterygote Insecta; there are 12-20 of them in Archaeognatha, 4-12 in Zygentoma.
The specialized rectal pads mentioned RFB 731 vary considerably in number and histology; they
may be consistently non-developed in endopterygote larvae.
Circulatory system, body cavity (RFB 527-528, 732-733). Traces of a segmentation (in the form
of paired ostia) of the anterior- and posteriormost portions of the dorsal vessel, if they were ever
present, must have become lost at a pre-hexapod level. The aorta is the dorsal vessel in front of the
ostium-bearing region.
The dorsal diaphragm referred to RFB 527 is composed of a one-layered epithelium associated
with muscle fibres arranged in a fan-wise fashion (spreading out towards the dorsal vessel), hence
their name alary muscles (which in RFB fig 16-7 is erroneously used for delicate fibres suspending
the vessel from the tergum); some of the fibres insert on the vessel while others extend across the
segment. Contrary to the dorsal diaphragm the ventral diaphragm is not an insect ground plan trait
but only evolved (more times independently?) within the Pterygota.
In cockroaches [kakerlakker] and mantids [knælere] there are in some segments lateral arteries
from the dorsal vessel, Fig 6A. It would be a straightforward assumption that such arteries are a
highly plesiomorphic feature, but they are unknown form other hexapods; hence they are apparently
an autapomorphy of the cockroach+mantid group, or more likely, the Dictyoptera as a whole, and
secondarily lost in termites.
Respiration (RFB 530, 733-735, fig 21-10). There is no evidence that the tracheal system in
hexapods was ever segmentally arranged in the head region and the abdominal apex. The apparent
groundplan complement of spiracles in Insecta comprises one-pair-per-segment on the mesothorx,
metathorax and abdominal segments I-VIII; the spiracles have a lateral position, those of the thorax
close to the anterior segmental borders11, those of the abdomen usually in the 'pleural membrane'
between tergum and sternum.
Some Diplura have as many as four spiracle pairs in the thorax, hence they cannot all be serially
homologous. Barlet (1988, Bull. Ann. Soc. roy. Belge Ent. 124: 171-187) has suggested that
hexapod spireacles pertain to no less than four series; the criteria for the identification of these need
renewed scrutiny, however. Note that Collembola-Symphypleona do have tracheae (one spiracle
pair in the neck region), and so do eosentomoid Protura (with spiracles on meso-and metathorax);
the text RFB 735 could be construed as meaning that all members of these 'orders' are devoid of
them.
The longitudinal tracheal connectives and the transverse commissures (RFB 733 and fig 21-10B)
are not hexapod or insect ground plan traits, but a likely groundplan autapomorphy of the
Dicondylia: in Archaeognatha the tracheae arising from one spiracle are unconnected with those
arising from adjacent spiracles, except that there are sometimes delicate transverse commissures in
the thorax.
Spiracular closing devices are said RFB 733 to be "usually" present. Closer muscles inserting
directly on sclerites in the abdominal spiracles have been considered a possible synapomorphy of
Odonata [guldsmede] and Neoptera; in adult Ephemeroptera [døgnfluer] the tracheal trunks just
inside the spiracles are closed through being compressed by body wall muscles. Intriguingly,
however, muscles inserting directly on the abdominal spiracles have actually been reported also
11
The first pair of thoracic spiracles often appears to be situated on the prothorax.
14
from some, but not all, Zygentoma (Rousset Int. J. Insect. Morphol. Embryol. 2: 55-80, 1973); a
parallelism?
The closing devices of the spiracles are obviously an adaptation to ‘advanced terrestrial life’. In
the case of apterygote hexapods that live in moist microhabitats water loss through the spiracles is
no serious hazard. Closing devices are secondarily lost in many advanced pterygotes (immatures in
particular) that live in moist or truly aquatic habitats.
Nervous system and associated endocrine organs (RFB 531-532, 735, 740, figs 16-11, 21-712,
21-8A, 21-15). If one recognizes the presence of a tetrocerebral segment in the hexapod head, then
the recognition of a ‘tetrocerebrum’in the cephalic central nervous system (in front of the
mandibular domain in the suboesophageal ganglion.) is a corollary. In the insect ground plan the
frontal ganglion (RFB fig21-7, Fig 2C here) is connected not only to the tritocerebrum, but also
has a nervous connection to the protocerebrum; this ‘nervus connectivus‘ has been lost
independently on more occasions in higher insects. Corpora cardiaca (RFB fig 21-7) are very
small in Archaeognatha and entognathans (may be entirely lacking in collembolans and DipluraCampodeidae, but that may well be secondary loss); in all hexapods they are closely associated with
the aorta wall, and are sometimes continuous with the later. Corpora cardiaca have on more
independent occasions become fused into a median formation. Corpora allata are in DipluraCampodeidae og apterygote insects distant from the c. cardiaca, but have convergently in other
entognathans and in Pterygota become closely approached to the latter. Primitively they are
innervated from the suboesophageal ganglion, but this innervation is lost independently on more
occasions within higher insects.
Sensory organs (RFB 533-537, 735-736, figs 16-12-13). The ommatidial structure of the faceted
eyes of Archaeognatha, Zygentoma (Fig. 7A here) and lower Pterygota and of the 'dispersed faceted
eyes' of Collembola is strikingly similar, and it has seemed straightforward to consider the presence
of two 'primary pigment cells' (derived from corneagenous cells) to be an autapomorphy of the
hexapod groundplan. The extant Diplura and Protura are (surely secondarily) eyeless.
Female reproductive system (RFB 736-737, fig 21-11). The many-ovariole-ovary type described
by RFB is characteristic of the Diplura-Japygina and the Insecta, while each ovary in Collembola,
Protura and Diplura-Campodeina is just a sac (Fig 9F). 'Out-group' comparisons with other
arthropods indicate that the last-mentioned configuration actually can be interpreted as the
plesiomorphic one (Stys, Zrzavý & Weyda 1993. Biol.Rev. 68: 365-379). RFB fig 21-11A shows
the ovarioles arising in a dense cluster from the lateral oviduct, but in the Diplura-Japygina (Fig.
9G) and some Insecta the ovarioles are arranged in a near-segmental manner along the duct; it has
been debated whether this is a genuine plesiomorphy.
RFB mention two ovariole types, one with "follicular nurse cells"13 supplying the developing
oocyte with yolk, and one without. The latter, which is believed to represent the insect ground plan
condition is called a panoistic ovariole (Fig. 6D), while the former are referred to as meroistic.
Meroistic ovarioles, in turn, also come in two forms, the polytrophic type in which each oocyte is
located next to the group of nurse nurse cells pertaining to it (Fig. 6E), and the telotrophic (or
acrotrophic) in which all nurse cells remain in the apical ovariole region, and the oocytes are
'nourished' through long cytoplasmic 'trophic cords'. The distribution of ovariole types is more
12
Note that in this figure the nervus recurrens, which is the unlabelled nerve that extends backwards from the frontal
ganglion, should have been shown continure behind the brain to reach the 'hypocerebral ganglion'.
13 Nurse cells are also referred to as trophocytes ['næringsceller']
15
complex than indicated by RFB. Telotrophic ovarioles have been evolved independently in
Ephemeroptera and a number of lineages within the putative Paraneoptera+Endopterygota clade, to
whose ground plan the polytrophic type is ascribed. The polytrophic type also occurs in
Collembola, campodeoid Diplura and Dermaptera; it is possible that in the last-mentioned order it is
a direct forerunner of that in Paraneoptera+Endopterygota. In some cases (Protura and a few
Antliophora) the apparently primitive panoistic type is interpreted as being secondary (Büning, J.
The Insect Ovary Chapman & Hall, 1994).
As mentioned above the position of the female gonopore is somewhat variable. In Ephemeroptera
the gonopores, opening just behind sternum VII are paired. Plesiomorphic condition or
specialization/character reversal?
It may be noted, that in some insects the female genital chamber ('vagina') anastomoses with the
rectum, forming a cloaca on the terminal true segment (morphologically segment XI).
The ovipositor formed by appendages on abdominal segments VIII and IX is a highly
characteristic autapomorphy of the ground plan of the Insecta; they have no counterparts in other
hexapods. The appendages in question are 'endites' - annulated in the case of the apterygote taxa on the coxopodites of the two segments in question (Fig. 11K), and as such are serial homologues
of the eversible sacs on pregenital segments. They are referred to as gonapophyses or as 1st (the
VIII pair) and 2nd (the IX pair) valvulae, respectively. The gonapophyses on each side are
interlocked by a tongue-and-groove arrangement, and tergal muscles inserted at their bases enable
them to make sliding movements whereby they can bore into a substrate. They enclose a cavity
through which the egg is moved, and small cuticular processes on their medial walls ensure that the
egg-movement is one-way only. Socalled 3rd valvulae (or gonoplacs) in winged insects are the
coxopodite and stylus IX (the uppermost appendage labelled IX in RFB fig 21-11B) which form a
protective sheath around the gonapophyses (and in the case of some orthopteroids become
functionally integrated into the ovipositor shaft).
Male reproductive system (RFB 737-738, fig 21-12). It is uncertain whether the clustered
arrangement of the testes follicles illustrated RFB fig 21-12A is ancestral in insects; a number of
overall generalized taxa have the follicles arranged along the sperm duct in a manner somewhat
reminiscent of the female ovariole arrangement illustrated in Fig. 9G.
As in several animal groups the ultrastructure of the spermatozoon (e.g. Fig. 7B) has proved
immensely diverse and phylogentically informative.
The male copulatory apparatus, phallus (or 'penis', a term used by some authors including RFB)
is very variably developed; it is probably generally formed by components (including limb
rudiments) of the ventral part of segment X, though elements from IX may participate as well. As
far as known all apterygotes have some kind of indirect sperm transfer14, hence the median tubular
'penis' in Archaeognatha illustrated Fig 11J is not an intromittent organ. In the archaeognathan (and
surely the insect) insect ground plan the phallic base is surrounded by short gonapophyses
pertaining to VIII and IX (they are lost in the family to which Nesomachilis, illustrated in Fig.11J,
belongs); these are homologues of the female ovipositor valves. Processes arising on/near the
phallic base, like those shown but not labelled in RFB fig21-12C may be homologues of these
gonapophyses in basal insects; such processes may be referred to as parameres. However, that term
is also used for the clasping appendages, which called claspers in RFB and which, as stated there,
are generally considered to be true limbs, i.e., homologues of the coxopodite+stylus in the insect
14
A few subordinate members of the Archaeognatha-Machilidae do deposit sperm on the female genitalia but not onto
the genital aperture; other closely related taxa do spin a carrier-thread on which the sperm is deposited.
16
ground plan; they are often referred to as gonopods. In the RFB diagram 21-12B only the stylus is
discrete; in such cases the coxopodite is believed be indistinguishably fused with sternum IX.
In Ephemeroptera [døgnfluer] and some Dermaptera [ørentviste] the phalli are paired. As in the
case of the ephemeropteran female gonopores it is debatable whether this is a genuinely
plesiomorphic condition or a specialization/character reversal. In most lower Neoptera there is no
tubular phallus, but the gonopore is flanked by two or more partly softwalled phallomeres, which
manipulate a spermatophore. A tubular phallus is usually present in Paraneoptera and
Endopterygota.
As mentioned by RFB the variablity of the male genital/postgenital segments is enormous; also
cerci and paraprocts may become modified and participate in copulation.
A formidable and largely order-specific nomenclature of the components of the male genitalia has been developed.
The same term may be used for non-homologous structures in different taxa, and conversely homologous structures in
different taxa may be referred to by different names. When using genitalia descriptions in morphological and taxonomic
literature one must, therefore, always familiarize oneself with the nomenclature adopted by the author(s) in question.
Egg (RFB 738). In addition to the properties of the egg-shell, chorion, mentioned by RFB it should
be mentioned that it also typically is provided with 'aeropyles' which permit exchange of respiratory
gases. Many terrestrial egg-shells locally form a 'plastron', a fine network whose mesh diameter is
small enough that the surface tension of water prevents it from penetrating when the egg is flooded
(which regularly happens, e.g., after rainfall).
Development (RFB 538-539, 738-740, figs 16-14, 21-13-15). The egg-cleavage pattern described
RFB 540 is probably not plesiomorphic in Hexapoda/Insecta. It has long been known that the
entognathan Collembola have an initially complete cleavage,i.e., the first daughter cells of the
zygote are separated by complete cell membranes and only later is a superficial blastoderm formed
as in other hexapods (and as shown for an arachnid in fig 16-14E). Interestingly, it is now known
that the Archaeognatha also have a (brief) initial phase of complete cleavage, but subsequently bell
borders in the inner egg region disappear, and a ‘normal’ blastoderm is formed (Fig. 8A); hence a
complete cleavage may indeed be a hexapod ground plan trait.
HEXAPOD PHYLOGENETIC SYSTEMATICS
On the role of fossils in systematic entomology
Assessments of the affinities and interrelationships among extant hexapods can be based on
comparisons which utilise a wider range of features than those provided by fossil forms. In 'easy'
cases where genuine synapomorphies abound and homoplasies are few or absent, interrelationships
between extant orders can be identified with a degree of certainty unattainable for fossil taxa.
However, increasing the amount of available comparative data does not always lead to ease in
phylogenetic decision-making. There are cases where the limited number of characters available to
the palaeontologist appear to support only a single phylogenetic pattern, yet, when additional
characters are studied in extant farms, their derived states are found to be distributed in a more
reticulate way. The neontologist thus finds the issue complicated by evidence for a variety of
possible phylogenies, of which only one can be true. On the other hand, neontologists, seeing
similar modifications in all extant taxa of a particular group, can be led to believe that these
modifications arose as a single evolutionary event. If the fossil record shows that extinct members
of the group lacked these modifications, then it may be that the neontologist's phylogenetic model is
oversimplified and the modifications arose more than once - the story of the subsegmented limb
vestiges on the pregenital abdomen of some Palaeozoic pterygotes is a good case. Hence, while
there are few cases where fossils have proved really helpful for clarifying relationships between
17
extant high-rank hexapod taxa, they have lead to the questioning of otherwise apparently wellsupported groupings.
Above all, palaeoentomology is outstandingly important for providing the only direct means of
assessing minimum ages and minimum geographical ranges of recognized monophyletic lineages and of course they can tell us about interesting 'organisation types' that are no longer with us.
THE PRIMARILY WINGLESS HEXAPODS
It is unquestioned that the absence of wings in the Collembola, Protura, Diplura, Archaeognatha and
Zygentoma is primary, and naturally all inquiries into the ground plan morphology of the Hexapoda
(if this entity is indeed a monophylum - if it is not, a quest for its ground plan is not meaningful)
and the Insecta have focussed on these groups. In pre-cladistic taxonomy they were united in a
taxon 'Apterygota' which is clearly paraphyletic in terms of the Pterygota, the winged insects15.
The apterygote hexapods may be broadly characterized as 'soil animals', though members of some
lineages live on top of the soil or litter, in vegetation, 'periphyton' etc. Hence almost all occur in
microhabitats characterised by high ambient moisture, reflected in their general possession of
water-absorbing regions ('eversible sacs'), lack of spiracular closer mechanisms, and reliance of
indirect sperm transfer by spermatophores or sperm drops which are deposited on various substrates
(including stalks or threads secreted by the male) from which the female subsequently takes it up
into its genital opening.
Apterygotes generally continue to moult after having become sexually mature.
The apterygote 'grade' of hexapods is only moderately species rich in the Recent fauna; only the
Collembola comprise more than a thousand described species. On the other hand, some apterygote
species may be immensely abundant in suitable habitats.
The entognathan hexapods: COLLEMBOLA, PROTURA AND DIPLURA
Alleged autapomorphies of a taxon 'Entognatha' comprising the above-mentioned taxa include:
'Entognathy' itself: the more or les s extensive overgrowth of the mouth-parts by 'oral folds' from
the lateral cranial wall, whereby the basal parts of the mandibles and maxillae come to be located
in 'gnathal pouches' (Fig. 7C). Malpighian tubules reduced to small papillae, or entirely absent.
Compound eyes degenerate in Collembola, entirely lacking in extant Diplura and Protura.
Absence of a centriole adjunct in spermatozoon has previously been considered a possible entognathan agroundplan
autapomorphy, but a formation of this kind is actually present in Protura (Jamieson et al. Insects. Their Spermatozoa
and Phylogeny. Science Publishers, Enfield 1999).
The Collembola, Protura and Diplura have had a chequered history in systematic entomology.
Much attention has been paid to the phenetic gaps that separate these three taxa from each other and
from the remaining hexapods (i.e., the Insecta), and they have sometimes all been ranked as
independent classes; Manton repeatedly asserted that entognathy had arisen independently in the
three entognathan 'orders'. However, the phenetic differences to which she alluded were considered
unconvincing evidence, and during the 1970s the view became widely adopted that these 'orders'
indeed constitute together a monophyletic class Entognatha, which has a sister-group relationship to
the Insecta; within the Entognatha a sister-group relationship was recognised between the Diplura
and a superorder Ellipura comprising the Protura + Collembola. Subsequent findings on fossils and
ovarian morphology led to entognathan monophyly again being questioned, and recent molecular
studies even suggest that the entognathans+Insecta assemblage is paraphyletic in terms of the
crustaceans, but these molecular phylogenies are in disagreement between themselves.
15
It remains, of course, legitimate and convenient to refer to the primarily wingless hexapods by the adjectival term
'apterygote(s)' even though a taxon name 'Apterygota' has had to be discarded.
18
'ELLIPURA' (= PROTURA + COLLEMBOLA) - a genuine monophylum?
Body size small (8 mm or less). Entognathy advanced: oral folds almost or actually meeting
posteromedially, maxillary palps small (3 segments or fewer) and labial palps minute (1segmented) when discemible. Posterior/ventral surface of head with median 'linea ventralis' (Fig.
7D), a groove with one or more longitudinal crests, extending from the openings of a set of labial
glands backwards onto the neck membrane in the Protura, and even to the preabdominal ventral
tube in the Collembola. Pretarsal claws unpaired. Cerci (limbs on hindmost abdominal segment)
absent. Abdominal spiracles absent
The two orders included here both have striking autapomorphies and hence are phenetically
distinctly set apart from each other as well as from other hexapods, but on the basis of the preceding
putative synapomorphies the monophyly of the Ellipura has for some time been widely accepted.
Absence of abdominal spiracles has been considered another ellipuran autapomorphy and may
indeed be valid as such, but it is admittedly difficult to determine the ancestral spiracle complement
of the Hexapoda. Unpaired pretarsal claws and absence of cerci have similarly been considered
potential 'ellipuran' autapomorphies, but this too is debatable. At present the monophyly of the
Ellipura is strongly challenged by molecular findings, see p. 23 below
COLLEMBOLA, springtails [springhaler]
Autapomorphies include small number (6) of abdominal segments and specialised appendages on
abdominal segments I (ventral tube, Figs 10C-D), III (retinaculum Fig. 10E) and IV (furca Figs
10A,C, F). Thoracic legs with long penultimate segment presumably representing a composite
tibiotarsus. Spirac1es cervical or completely absent.
The unique abdominal segmentation confers upon the Collembola an extreme phenetic isolation
within the hexapod (indeed mandibulate) assemblage. It is possible, but of course conjectural, that
ancestral Collembola were highly anamorphic and that lack of postembryonic segment addition is
an autapomorphy. Manton (e.g. The Arthropoda. Habits, functional morphology, and evolution.
Clarendon Press, Oxford. 1977) emphasised the uniqueness of collembolan trunk design and related
it to the hydrostatic jumping mechanism as known in detail in a tomocerid springtail; possibly, this
character complex will prove autapomorphic for 'ordinal' ground plan. In repose the furca is flexed
under the abdomen and is held in place by the retinaculum. Release of the grip of the retinaculum
leads to the furca swinging downwards-backwards, propelling the animal forwards. The swing of
the furca during jumping is a movement primarily due to locally increased blood pressure in the
abdominal cavity.
The more or less densely clustered simple eyes represent dispersed ommatidia of compound eyes.
A sometimes prominent, variably shaped and sculptured surface structure (the 'postantennal organ')
behind the antennae is a chemoreceptor.
Collembolans are mainly detrivores and fungivores; herbivores and carnivores do occur. Some
species may occur in huge abundance and collembolans play an important role in nutrient cycling in
soil ecosystems.
Respiration in most Collembola takes place across the general body surface; the
SYMPHYPLEONA have tracheae issuing from a single pair of spiracles located in the neck
membrane - a unique situation in hexapods.
Concerning egg cleavage: see above under Ontogenesis.
There are 7000+ described species of Collembola, 400+ are known from N. Europe. Classification
is unstable. One monophyletic assemblage is the SYMPHYPLEONA characterized by a swollen
globular trunk with segmental borders largely obsolete (Fig 10A). They are often strongly
19
pigmented and live on the soil surface or in vegetation; here belongs a cosmopolitan agricultural
pest Sminthurus viridis ['lucerneloppe'].
Symphypleonans are also notable for their often very elaborate reproductive behaviour; males may have antennae
modified for grasping the antennae of the (considerably larger) female, and they are carried around by the latter until
she finds a site suitable for him to deposit his spermatophore (Fig. 10B).
The non-symphypleonans come in many forms. One major assemblage, the (monophyletic?)
PODUROMORPHA, is characterized by retaining a well developed prothorax. In another, the
(monophyletic?) ENTOMOBRYOMORPHA the prothorax is much reduced, dorsally covered by
the metathorax. Members of the former generally are smaller and have shorter limbs than the
entomobryomorphans, and many have the jumping apparatus reduced, particularly among the
minute taxa living in deep soil; such taxa may be completely unpigmented. In contrast,
collembolans living on soil (or water) surface or in vegetation may be strongly pigmented and they
may have elaborate vestitures of scales or hairs.
PROTURA
Tentorium, visual organs and antennae absent. Fore legs enlarged, usually carried lifted and
anteriorly directed, richly furnished with sensilla. Abdominal limbs minute, their occurrence
restricted to 3 anteriormost segments. Telson (12th 'segment') distinct in adult - plesiomorphy?
The absence of antennae immediately set the Protura apart from other hexapods. indeed from
other mandibulate arthropods. Evidently the long fore legs have taken over their sensory function.
Proturanss are also unique among hexapods in having anamorphosis (a phenomenon also
encountered in some other mandibulate arhropods), i.e., the newly hatched immatures have fewer
abdominal segments than the adult. The earliest known instars have nine segments, and the three
posterior segments are added in some of the following moults.
The position of the gonopore on segment XI in both sexes is again a unique trait among hexapods.
The families in EOSENTOMOIDEA (families EOSENTOMIDAE and the E Asian
SINENTOMIDAE) have spiracles situated on the meso- and metathorax. The other proturans are
grouped together in the superfamily ACERONTOMOIDEA; they are all non-tracheate.
Proturans are tiny (never exceeding 3 mm), mostly unpigmented soil animals which mostly feed
on fungus hyphae.
About 700 species are described, very few (10+) are known from N. Europe, both main groupings
being represented here.
DIPLURA
Head with neither tentorium nor ocelli (absence of compound eyes in extant families apparently not
resulting from a single loss event). In mouthparts maxillary galeae interlocked with superlinguae16
(Fig. 9D). Thoracic legs reportedly with unique development of trochanteral femur-twisting muscles
and a similarly unique pivot at the femur-tibia joint (Figs 9E, I). Gonopore situated immediately
behind sternum VIII in both sexes.
While the monophyly of the Diplura was arguably never strongly supported (and is contradicted
by the diversity in ovariole structure, see pp. 14 and , Figs 9F-G), the above-mentioned peculiar
specialization (known since long, but largely overlooked) is an apparently strong autapomorphy of a
taxon comprising the CAMPODEIDAE and JAPYGIDAE.
The head structure in the U. Carboniferous Testajapyx (Fig. 9J), whose assignment to the japygid
lineage seems well founded, demonstrates not only that the absence of eyes must be discarded as a
dipluran autapomorphy, but that a partially degenerate compound eye was part of the entognathan
16
The small paired appendages of the hypopharynx that also occur in basal Insecta (illustrated for an archaeognathan
in Fig. 11E).
20
groundplan. Similarly, the relatively lang and multiarticulated maxillary and labial palps of
Testajapyx demonstrate that the extreme palp reduction seen in extant entognathans cannot be a
groundplan autapomorphy of the group as a whole.
800+ species described. The largest family is the JAPYGIDAE (ca 400 species) whose cerci are
strongly sclerotized pincers (with segmentation obliterated), whose posterior abdominal segments
are also strongly sclerotized/melanized (Fig. 9A), and whose abdomen are entirely devoid of
spiracles. Together with a couple of small, obviously closely related families they constitute the
‘suborder’ DICELLURATA. The ‘suborder’ RHABDURA comprising all other diplurans is likely
non-monophyletic; its principal family is the CAMPODEIDAE (350+ species) with unmelanized
trunk and long filiform cerci (Fig. 9C).The few and small other families included have the cerci
short and stout, but still distinctly segmented (Fig. 9B, illustrating a member of the
ANAJAPYGIDAE). Only campodeids and japygids are well studied; the alleged dipluran
groundplan autapomorphies need to be checked in representatives of the smaller ‘rhabduran’
families.
It is very noteworthy that campodeids have 3 pairs of thoracic spiracles, and japygids as many as
4; in the last-mentioned case, therefore, the spiracles cannot all be serially homologous.
Dicelluratans are carnivorous, using the cercal pincers to catch prey animals; the group comprises
the largest apterygote hexapods (a few taxa exceeding 50 mm). Rhabdurans are omnivorous, eating
many kinds of organic material, and they may be active carnivores as well.
Only the CAMPODEIDAE are represented in N. Europe (with 10+ species, less-than-acentimetre long).
INSECTA (=ECTOGNATHA)
Antenna with its lack of muscles beyond the scape (first segment) and the presence of a large group
of chordotonal organs ('Johnston's organ') in the pedicel (second segment). Posterior tentorium
developed, forming a transverse bar. Coxae of thoracic legs primitively without articulation with
sternum; tarsi subsegmented, and pretarsal claws articulate on distal tarsomere instead of on
pretarsal base (Boudreaux Arthropod Phylogeny with Special Reference to Insects. Wiley & Sons,
New York etc., 1979). Fema1es with ovipositor formed by gonapophyses (limb-base endites) on
segments VIII and IX. Long, annulated 'terminal filament' developed from dorsum XI (plus telson
?). The spermatozoon has 1-3 'accessory bodies', developed from the centriole adjunct (Jamieson et
al. 1999). During early embryogenesis the germ band comes to be located within an amniotic
cavity.
A characteristic complement of spiracles (one segmental pair from mesothorax to abdominal
segment VIII) may be ascribed to the insect ground plan (though abdominal spiracle I is absent in
the Archaeognatha); a segment VIII spiracle does not occur elsewhere in hexapods, but it cou1d be
plesiomorphic at this level.
The monophyly of Archaeognatha + Zygentoma + Pterygota seems very well founded and is
apparently now universally agreed upon. The Archaeognatha and Zygentoma are the primitively
apterygote insects; they are superficially somewhat similar and they have formerly been united in
the taxon 'Thysanura'. However, there are good reasons for considering the Zygentoma to be the
cladistically closest relatives of the Pterygota, and these two groups are therefore now united in the
taxon Dicondylia.
ARCHAEOGNATHA [klippespringere]
Compound eyes enlarged, medially contiguous. Spiracles on I absent.
The two aforementioned traits establish the monophyly of this small 'order'. Moreover, it seems
likely that elaborate jump-facilitating specialisations in abdominal skeletomuscular structure
21
described from various machilid genera will prove to be characteristic for the entire order. It is
difficult to assess which of the order's other peculiarities (such as the fact that their glossae and
paraglossae are bilobed) are actually apomorphies.
The mature sperm axoneme has the outer 'singlets ' arranged in two groups as in the Diplura-Campodeidae; this
condition is now considered to have been evolved as parallelisms in the two groups. (Jamieson et al. Insects. Their
Spermatozoa and Phylogeny. Science Publishers, Enfield 1999).
See Fig. 11 for general facies and several structural details. Archaeognathans are overall uniform.
They mostly live on rocks from which they scrape algae, lichens etc. There are some 500 described
archaeognathan species worldwide, just a few in N. Europe. Our best known species belong to
Petrobius and occur on coastal rocks, moles etc.
Recent comprehensive account: Sturm, H. & Machida, R: Archaeognatha. Handbook of Zoology
IV, 37, de Gruyter 2001)
DICONDYLIA
Mandible with secondary (anterior) articulation acquired in addition to the primary posterior one;
in the new (and initially somewhat loose) articulation a cranial process fits a mandibular concavity.
Maxillary palp reduced in size, distinctly smaller than thoracic legs. Endoskeletal rods from
hypopharynx ('fulcra' or 'fulturae', formations present in diplurans and archaeognathans and
therefore ascribed to the insect ground plan) suppressed. Postoccipital ridge17 complete.
Gonangulum18 in ovipositor base fully developed, with the typical articulations present. Abdominal
tracheal system with segmental commissures and intersegmental connectives.
Some further putative dicondylian autapomorphies may prove valid. The basic tarsomere number
(including 'basitarsus') of the thoracic legs is probably five (if the five-segmented condition in
Tricholepidion is not autapomorphic, as believed by some). Temporary closure of the amniotic
cavity during early embryogenesis could be another dicondylian autapomorphy.
A purely superficial egg cleavage may constitute an additional synapomorphy of Zygentoma and
Pterygota.
ZYGENTOMA, silverfish etc. [sølvkræ-gruppen]
The monophyly of an assemblage comprising all non-pterygotan Dicondylia (families
LEPIDOTHRICHIDAE, NICOLETIIDAE, MAINDRONIIDAE and LEPISMATIDAE) is very
uncertain. Previously proposed putative synapomorphies in labial palp structure and 'sperm
conjugation' have recently proved to be questionable or downright spurious, and the loss of
hypopharyngeal superlinguae (still retained in the pterygote ground plan) is a weak character (like
regressions in general). At present zygentoman monophyly is primarily supported by a specialized
articulation between the cercal base and tergum X (see Koch Entomologische Abhandlungen 61:
122-125, 2004 for an update on)
The western Nearctic Tricholepidion gertschi, sole extant member of the family
LEPIDOTHRICHIDAE, has retained a number of apparently primitive traits (including large
abdominal sterna with posteriorly attached coxopodites, large number of pregenital styles and
17
An internal ridge (counterpart of an external groove) on the cranium bordering the posterior foramen; it may be more
or less completely obliterated again in subordinate pterygotes.
18 The gonangulum is a small, often near-triangular sclerite in the base of the ovipositor of dicondylian insects. It
typically has three articulations, viz, with the base of the gonapophysis VIII, the base of gonapophysis IX, and the
anterolateral corner of tergum IX, respectively. In subordiante pterygote lineages the gonangulum may become fused
with one of the adjacent sclerotizations. Archaeognathans may have a tiny sclerite - a gonangulum forerunner? - in a
position corresponding to that of the dicondylian gonangulum, but it has none of the articulations characteristic of the
latter.
22
eversible sacs) not found in other Zygentoma, let alone pterygotes. It is particularly remarkable that
Tricholepidion also has retained the cephalic, ligamentous endoskeleton, unlike any other examined
dicondylians. It is possible, therefore, that Tricholepidion is the sister group of all other Dicondylia
and should be given ordinal rank. On the other hand, Tricholepidion and the NICOLETIIDAE share
a probably apomorphic type of sensilla on the terminal filament.
Koch's recent finding that the anterior and posterior tentorial arms in MAINDRONIIDAE are
fused as in winged insects is a surprise. Evidently this again leads one to question zygentoman
phylogeny.
The zygentoman assemblage comprises altogether 400+ described species, in N. Europe a couple
of synanthropic species including the very familiar silverfish Lepsma saccharina [sølvkræ, sølvfisk]
which feeds from many kinds of organic matter and may be a minor household pest.
The apterygote hexapods and hexapod 'deep phylogeny'
The 'conservative' proposal of the basal dichotomy in the Hexapoda being between the abovementioned taxon 'Entognatha' and the Insecta was challenged on the basis of the ovary structure (see
p.14 above), which suggests that Diplura-Campodeina are the sister group of Collembola+Protura
and/or that the Diplura-Japygina are the sister group of the Insecta (Štys, Zrzavý & Weyda, Biol.Rev. 68: 365-379, 1993).
An alternative challenge of the conservative phylogeny came from Kukalova-Peck's claim that it
is a synapomorphy of the Diplura (which she recognizes a monophylum) and the non-entognathan
hexapods that the abdominal limb bases, inclusive of the trochanter, have been incorporated into the
abdominal wall, whereas, in the groundplan of the Collembola + Protura assemblage only the
subcoxa has been incorporated; this interesting suggestion awaits further documentation and
evaluation. But the suggestion that the closest relationships of the Diplura are with the nonentognathans naturally leads to a reconsideration of the significance of characters that have
previously been ascribed to the hexapod groundplan and secondarily modified in the Collembola +
Protura, viz. the paired pretarsal claws, filiform cerci and details of axoneme structure in the sperm.
While it appears debatable whether the paired pretarsal claws in Diplura and Insecta were an apomorphy or a
plesiomorphy (out-group comparisons from other arthropods give no unabiguous answer) they would clearly be
attributed to the hexapod ground plan in the conventional hypothesis of hexapod phylogeny being represented as Insecta
+ (Diplura + (Protura + Collembola)). With entognathan monphyly being questioned the secondary nature of unpaired
claws in Collembola and Protura is less obvious.
The cerci, i.e., the limbs of segment XI, are phylogenetically enigmatic structures. They are filiform in DipluraCampodeidae (shortened or forcipate configurations in other Diplura generally are considered secondary), in
Archaeognatha, Zygentoma and primitive pterygotes, and it has therefore seemed straightforward to attribute filiform
cerci to the hexapod groundplan. Viewing this character in isolation it would, of course, be more parsimonious to
consider it synapomorphic of the Diplura + Insecta only, thereby obviating the need for postulating a secondary
reduction in the Collembola + Protura. However, the issue is further complicated by the above-mentioned finding that
in some Palaeozoic insects the cerci are overall similar to the rather short preceding abdominal limbs and have retained
paired claws.
Sperm evolution of the basic hexapods is discussed in detail by Jamieson et al. (Insects. Their Spermatozoa and
Phylogeny. Science Publishers, Enfield 1999). A sperm axoneme with a ring of nine doublets surrounding a central pair
of tubules (i.e., the '9+2' pattem) is probably plesiomorphic within the Arthropoda. Collembola have a 9+2 pattern.
Protura lack the central tubules and can have axoneme patterns such as 12+0 or 14+0. The Diplura-Campodeidae, like
the Archaeognatha, Zygentoma (Fig. 7.B) and most Pterygota have a ring of nine single tubules peripheral to the nine
'doublets' of the basic sperm axoneme, leading to the formation of a '9+9+2' configuration, which has been attributed to
the hexapod groundplan. If a 9+9+2 configuration is part of the hexapod groundplan, then the patterns in Collembola
and Protura would have to be the results of secondary reductions. The 9+9+2 type could altematively be considered
synapomorphic of the Diplura + Insecta, obviating the need for postulating a secondary reduction in the Collembola +
Protura. A postulate of this kind would still be necessary to explain the 9+2 pattem of Diplura-Japygidae, if the Diplura
are indeed monophyletic.
Counterparts of the myriapod 'Tömosvary's organ' are retained on the head of Collembola
23
('postantennal organ') and Protura ('pseudoculus'); their absence in Diplura and Insecta could be
considered synapomorphic.
Recent analyses of extensive sets of morphological data (Bitsch & Bitsch Zoologica Scripta 29:
131-156, 2000; ibid. 33: 511-550, 2004) consistently retrieve the Insecta and Dicondylia as here
circumscribed, but the Zygentoma, Diplura, Entognatha and Ellipura may or not be retrieved
depending on analytical protocols.
A study based on the entire mitochondrial genome recently startled the entomological community
by finding the hexapods to be non-monophyletic: collembolans were outside a clade comprising the
crustaceans and remaining hexapods (Nardi et al. Science 299: 1887-1889, 2003; see subsequent
discussion by Delsuc et al. Science 301: 1442, 2003; Nardi et al. Science 301:1482d-1482e, 2003;
Bitsch et al. Systematic Entomology 29: 433-440). A subsequent study (Giribet et al. Organisms,
Diversity & Evolution 4: 319-340, 2004) based on combined analysis of five molecular markers and
an extensive morphological data set perhaps even more surprisingly had stable support for a
monophyletic Diplura+Protura (a grouping never proposed on morphological grounds) and most
surprisingly of all, had this group outside a clade comprising Collembola, Crustacea and Insecta.
Yet another molecular study (Regier et al. Ann. ent. Soc. Amer. 97: 411-419, 2004) based on three
nuclear genes but with a quite modest taxon sampling disagreed with the previously mentioned
morphological or molecular studies in retrieving a "modestly well supported'' monophyletic
Archaeognatha+Zygentoma (i.e., the old 'Thysanura').
The interrelationships of the basal hexapod lineages are, then, currently open to debate to a degree
hardly predicted by the turn of the millennium.
PTERYGOTA, the winged insects
Meso- and metathorax in mature stage(s) bearing wings with a venation and basal articulation that
can apparently be derived from a single patter. Pleura of wing-bearing segments high and well
sclerotised, stiffened by internal ridge from pleural wing process to coxal articulation. Pre- and
metatentorium fused. Abdominal eversible sacs lost ( somewhat similar formation present plesiomorphy, character reversal or neoformation? - on venter I in Grylloblattodea). Non-cuticular
trunk endoskeleton absent.
There is now broad agreement on the monophyly of the winged insects. The morphological basis
for wing development continuously attracts much attention: the 'wing-from-leg-base-exite' theory
mentioned p. 11 above (and see Fig. 4A) has gained some acceptance, while other workers still
favour a conservative ‘paranotum theory’: A ‘paranotum’ (or ‘paratergite’) is a lateral expansion of
the tergum (and the accompanying membranous body wall on its lower side which overhangs the
pleuron – basically similar to the laterally expanded thoracic terga in extant Archaeognatha and
Zygentoma. The traditional idea of wing evolution is that zygentoman-like pterygote ancestors
(whch climbed vegetation) acquired a line of flexible cuticle at the base of a tergal expansion of this
kind; this conferred some mobility upon the lateral tergal portion and enabled flapping movements
when gliding (for a modern presentation of this line of reasoning see Hasenfuss J. Zool. Syst. Evol.
Research 40: 65-81, 2002).
The wing-bearing thoracic segments of pterygote insects are profoundly modified, see Fig 13. The flight
motor requires that the pleura are high, and that the thoracic 'box' is largely stiffened. The pleural
sclerotization is one large plate (in which the ancestral transverse division may remain more or less
identifiable) which ventrally has an articulation with the coxa, while its dorsal margin is produced
into the pleural wing process (WP) [pleurale vingetap] which articulates with a sclerite in the wing
base. A prominent linear cuticular thickening, the pleural sulcus (PlS), extending between the coxa
and wing articulations stiffens the pleuron; the pleural areas in front of and behind this sulcus are
referred to as the episternum (Eps) and the epimeron (Epm), respectively. An internal apodeme on
24
the pleural sulcus may have a muscular connection to, or be completely fused with, a prominent
sternal apodeme (Fig 13C, SA2).
In pterygotes the pterothorax (sometimes the prothorax as well) often has the pleural sclerotization
and sternum anteriorly fusing into a 'precoxal bridge' (rcx); sometimes also a postcoxal bridge is
formed. It may, then, be difficult or impossible to decide how much of the ventral plate is actually
pleural; some insect morphologists even believe that all anterior 'tergosternal' muscles in most
pterygotes actually are morphologically tergopleural.
The design of the wing veins [ribber] has profound consequences for the mechanical properties of
the wings, and diversity in this pattern (the 'venation' [ribbenettet]) has long-standing use in insect
systematics; hence vein names are required knowledge for entomologists (Figs 13B, 15). The
principal ones, the longitudinal veins [længderibber] have a course roughly parallel to the long axis
of the wing, and they have a presumably primitively dichotomous branching pattern. From front to
back they are costa (C) (which may be confluent with the fore margin of the wing), subcosta (Sc),
radius (R), radius (or radial) sector (Rs), media (M), cubitus (Cu)19and analis (A)20 (of which there
may be a variable number). There is no general agreement on the number of branches of the
longitudinal veins in the ground plan of the insect wing, but a pattern like the one depicted in Fig.15
is probably not far off the mark. R and Rs have a common stem in almost all extant pterygotes, and
even more posterior veins may be shifted forwards and added to this stem. Variation in the venation
may come in the form of reductions, fusions/anastomoses of veins, but some cases of particularly
rich peripheral branching may also be derived. The longiudinal veins may be connected by a more
or less rich complement of transverse veins [tværribber] which unlike the principal longitudinal
veins usually (though not consistently, as once believed) are devoid of tracheae.
The veins are not the only important structural elements of insect wings. Also elaborate systems of
'fold lines' and 'flexion lines' influence the mechanical properties of the wings; they may cause
specific deformations of the wing during the stroke cycle and (in neopterans) may enable specific
folding patterns of the wing in the resting position.
The tergum above the wing base is produced into an anterior notal wing process (Fig 13A, ANP) ,
a posterior notal wing process (Fig 13A, PNP), and one or more median notal wing processes. The
wing-trunk-articulation area is very structure-rich and is one of the body regions that is most
difficult to study, particularly in small and weakly sclerotized/melanized insects. Small wing base
sclerites articulate with tergal/pleural processes on one hand and with bases of principal wing veins
on the other. While interpretations of the wing base in the most primitive fossil pterygotes and the
extant Ephemeroptera [døgnfluer] and Odonata [guldsmede] is difficult (and remains controversial),
the wing articulation in neopterans is practically always compatible with the model shown
diagramatically in Fig 13B. The 1st axillary [axillare 1], 1Ax ,articulates proximally with the
anterior and median notal wing processes, and distally with Sc. The 3rd axillary [axillare 3], 3Ax,
articulates with the posterior notal wing process and the anal vein group. The 2nd axillary [axillare
2], 2Ax, is a very complex formation comprising sclerotizations in both the upper and the lower
wall of the wing; it articulates with the two preceding axillaria, and its ventral part articulates with
the pleural wing process. The more or less distinctive median plates (m, m’) are situated between
axillaria 2/3 and the media-cubital veins. It is contraction of a pleural muscle (Figs 13B-D: D)
inserting on the 3rd axillary that draws a neopteran wing backwards-inwards to the resting position;
the movement is accompanied by the formation of a dorsally convex fold between the median
19
The posterior Cu branch has by some workers been considered an independent vein named postcubitus; hence the
abbreviation ‘Pcu’ in Fig. 13B
20 The anal veins are by some workers referred to as vannal veins (from vannus, a fan); hence the abbreviations “V” in
Fig. 13B.
25
plates, while the postero-proximal wing area, the jugum (Ju), is turned upside down. The
membranous area below the wing contains a sclerotization, the basalare (Fig. 13A, a), in front of the
pleural wing process (it may be more or less extensively synscleritous with episternum), and
another, the subalare, (Fig. 13A, Sa) behind the process.
The indirect wing muscles are shown in Fig.13C: C is an indirect levator, mA an indirect
depressor; the latter often inserts on large plate-like infoldings, phragmata (Fig13A, Pph; 13C,
1ph, 2Ph) from the dorsal intersegmental borders. The muscles referred to RFB 727 as direct
[flight] muscles (Fig. 13D, “E muscles”) actually insert on the basalare and subalare (in some
subordiante lineages a pleural muscle also inserts on the 1st axillary). There will not be general
agreement with their statement that "early flying insects lacked indirect muscles". Extant
Ephemeroptera [døgnfluer] do have well developed dorsoventral indirect wing levators and
dorsolongitudinal indirect wing depressors, and these muscles also do have homologues in
apterygote insects. The weak development of the indirect wing depressors in dragonflies,
cockroaches etc. may well be secondary conditions. Fig. 14 here shows diagrammatic cross-sections
of the pterothorax in some pterygotes with different flight motors.
Pterygote ‘deep phylogeny’. Only three of the basic pterygote lineages have survived to the
present, viz. the Ephemeroptera, the Odonata and the Neoptera. It has been commonplace to unite
all non-neopteran pterygotes, extinct and extant, in a taxon 'Palaeoptera', but there has been
considerable uncertainty about whether this is monophyletic or not.
The venations of extant Ephemeroptera and Odonata are obviously different, but same Palaeozoic
fossilsis assigned to the two lineages are phenetically very similar, and the formation of a basal
wing brace through an anastomosis of the anterior anal vein with the posterior cubitus is considered
a synapomorphy of the two (Kukalova-Peck Canad. J. Zool. 63: 933-955, 1985). The anastomosis
in modern dragonflies (SAE21 Fig. 17.4) has been interpreted to lie at the lower end of the so-called
'anal crossing' (which, then should actually be CuP), whereas the anastomosis area in modem
mayflies is secondarily desclerotised. According to Kukalova-Peck's wing interpretation, it is a
synapomorphy of the ephemeropteran-odonate lineages plus the extinct Palaeoptera that the media
always has a basal stem, while in same subgroups (and hence in the groundplan) of the Neoptera
MA and MP are still separate at their bases. These characters provide the principal morphological
arguments for accepting a monophyletic taxon Palaeoptera.
On the other band there is evidence from the fossil record (Kukalova-Peck Canad. J. Zool. 61, 1983) that the
shortened, bristlelike antennal flagella characteristic of modern mayflies and dragonflies cannot be ascribed to their last
common ancestor. Moreover, while the aquatic lifestyle of ephemeropteran/odonatan immatures is usually considered to
be derived, this is at least debatable.
Evidence from extant representatives of the basic pterygote lineages provides some support for
the alternative assumption of a sister-group relationship between the Odonata and the Neoptera.
Both are characterised by the absence of a moult in the imaginal (i.e. fully winged) stage, and it
seems very straightforward to consider it to represent an ancient condition. It must be noted,
however, that the fossil record allegedly indicates that moulting of flying stages has been
independently eliminated within several pterygote lineages, including the Neoptera (see again
Kukalová-Peck’s review chapter on fossils, pp. 141-179 in CSRIO [ed] The Insects of Australia 1,
Melbourne University Press 1991). The tracheation of each wing and pterothoracic leg includes a
component connected with the spiracle of the following segment. Occlusor muscles inserting
directly on abdominal spiracular sclerites are present in same (but not all) Odonata and generally
(and surely primitively) in the Neoptera, but they are lacking in Ephemeroptera, as in the primarily
apterous insects (but note the reservation about some Zygentoma mentioned p.13). A more detailed
21
Naumann (ed.) Systematic and Applied Entomology, cf p 26.
26
reassessment of this odonatan/neopteran similarity is needed. The anterior mandibular articulation is
firm in the Odonata and Neoptera, whereas in Ephemeroptera, as in Thysanura s.str., an ample
articular membrane permits considerable freedom of movement. Hypopharyngeal lobes in Odonata
or Neoptera may never be true superlinguae (although at least in the case of same Plecoptera the
issue remains debatable), while these primitive formations, occurring in scattered groups of nonpterygote hexapods, are prominent in the groundplan of nymphal Ephemeroptera. Similarly, a long
terminal filament is retained in Ephemeroptera, but nowhere else in pterygotes; the homology (and
hence plesiomorphy) of the posteromedian gill filament (SAE fig. 18.6) in nymphs of a few
Plecoptera-Austroperlidae remains questionable. Further loss characters shared by the Odonata and
Neoptera include all tentoriomandibular muscle bundles except one, the tentoriolacinial muscle and
probably some pterothoracic muscles. The absence of a common radial stem in some
Ephemeroptera has been considered uniquely primitive in winged insects, but some workers
attribute the same condition to the odonatan lineage (and also the exticnt palaeodictyopteroids) on
the basis of evidence from fossils. The paired female gonopores in some female Ephemeroptera
have similarly been considered uniquely primitive within pterygotes, but others, probably correctly,
consider them a secondary feature. According to the latter view the primitive condition in the order
is exhibited by those taxa that have a median vestibulum into whose anterior end the gonoducts
open (recalling conditions in non-pterygote insects).
If the evidence for the monophyly of both the Odonata plus Ephemeroptera and the Odonata plus
Neoptera is inconclusive, the same is certainly also true of the putative ephemeropteran/neopteran
synapomorphies suggested by earlier workers. Perhaps the best known argument concerns sperm
transfer, which in the Odonata is still, in a sense, 'indirect'; the gonopore-to-gonopore can, then, be
considered a shared derived character of Ephemeroptera and Neoptera.
The argument from mandibular structure (see above) for the monophyly of Odonata+Neoptera
has been emphasized recently (e.g., Staniczek, Zool. Anz.239: 147-178, 2000). In contrast, rDNA
data (Wheeler et al. Cladistics 17: 113–169, 2001; Hovmøller, Pape & Källersjö Cladistics 18:
313-323) support ‘palaeopteran’ monophyly.
The conclusion seems inescapable the problem of the basic dichotomy in extant pterygotes cannot
be solved without postulating disturbing homoplasy one way or another.
THE FOLLOWING SECTIONS ON INDIVIDUAL ‘ORDERS’ OF WINGED INSECTS
ARE JUST COMMENTS ON/ADDITIONS TO THE TREATMENTS OF THESE TAXA IN
I. D. NAUMANN (ED.) SYSTEMATIC AND APPLIED ENTOMOLOGY, MELBOURNE
UNIVERSITY PRESS 1994; IT IS REFERRED TO AS “SAE”
EPHEMEROPTERA, mayflies [døgnfluer] SAE 124, 248-253
Note the paired male copulatory organs and female gonopores in the ordinal ground plan.
In Danmark about 40 species.
ODONATA, dragonflies [guldsmede] SAE 124, 254-261
The ‘suborder’ ZYGOPTERA (damselflies [vandnymfer]) has been considered paraphyletitic in
terms of ANISOPTERA [egl. guldsmede], but it may actually be monophyletic. The small Asiatic
genus Epiophlebia has ‘zygopteran’ traits in ving morphology, but the body design and nymph
morphology is anisopteran-like; it is usually placed in a high-rank taxon of its own,
ANISOZYGOPTERA.
Most Danish ‘vandnymfer’ pertain to the family COENAGRIIDAE, while the largest and most
strikingly coloured (the males have blue-pigmented wings) are in the AGRIONIDAE. Our largest
27
anisopteran families are AESHINIDAE (common large species in Aeshna) and LIBELLULIDAE
(large, stout-bodied taxa in Libellula, moreover some genera with smaller and more slender
members). Altogether about 50 odonatans occur in Danmark, 30+ being anisopterans.
There are many regional and national manuals on dragonflies. Ole Fogh Nielsen's information-rich
and beautifully illustrated De Danske Guldsmede, Apollo Books, 1998 is the main national
reference.
Lower Neoptera, or 'orthopteroid' orders SAE 124
As expounded in SAE 124 the phylogenetic relations between these orders are difficult to resolve
Kukalová-Peck's optimistic, largely resolved phylogeny (SAE chapter 6, later elaborated on in Can.
J. Zool., 70: 2452-2473, 1992 and Syst. Ent. 18: 333-350, 1993) is controversial (Kristensen Zool.
Beitr. 36: 83-124, 1995). A 'total evidence' analysis of insect phylogeny on the basis of rDNA and
morphological characters (Wheeler et al., Cladistics 17: 113-169, 2001) ends up with a somewhat
resolved phylogeny of the lower neopterans, which (perhaps surprisingly) here constitute a
monophyletic entity: ((Plecoptera + Embiotera) + (Phasmatodea + Orthoptera)) + (Dermaptera +
Grylloblattodea + Zoraptera + Dictyoptera); however, the morphological dataset used in that
analysis is much in need of revision. An analysis of a smaller, but more reliable morphological
dataset (Beutel & Gorb, J. zool. Syst. Evol. Res. 39: 1-31, 2001) does find the assemblage of lower
neopteran orders to be paraphyletic in terms of the Paraneoptera and Endopterygota. The recently
described Mantophasmatodea may be most closely related to the Grylloblattodea; this suggestion,
initially made on the basis of the foregut sclerotization, has been supported by subsequent
molecular findings (Jarvis & Whiting Ent. Abhandlungen 61: 146-147, 2003).
ORTHOPTERA= SALTATORIA [græshopper] SAE 126, 290-296
The characteristic orthopteran jumping mechanism, an extension of the femur-tibia joint, is
paralleled in, e.g., the so-called flea beetles ([jordlopper] a subordinate lineage within the
Chrysomelidae [bladbiller]). In contrast, the great majority of other jumping insects the jump is due
to a rotation of the trochanter relative to the coxa – the same movement by which winged insects
take off for flight.
The two generally recognized suborders are ENSIFERA [løvgræshopper i videre forstand] with
the superfamilies Gryllacridoidea, Tettigonioidea and Grylloidea [fårekyllinger]) and CAELIFERA
[markgræshopper] including the rest. Some Orthoptera systematists have insisted that the Ensifera
and Caelifera should be treated as distinct orders, but the question remains whether the Ensifera are
paraphyletic in terms of the Caelifera. Probably the best argument for ensiferan monophyly is a
peculiar tooth arrangement in the posterior (proventricular [tyggemave]) section of the fore gut. The
ensiferan ovipositor (Figs 16A-C) has a strikingly apomorphic structure, in as much as the 3.
valvulae (normally a protective sheath around the functional ‘shaft’ comprising the interlocked 1st
and 2nd valvulae) here are integrated in the ‘shaft itself, being also interlocked with the 1st and/or 2nd
valvulae. However, the caeliferan ovipositor (SAE fig. 1.24D) is so pronouncedly autapomorphic
(the short valvulae are free from each other and can perform outward-directed digging movements),
that it is difficult/impossible to decide whether it has been derived from a primitive the ‘ensiferantype’ ovipositor.
There just above a dozen ensiferans in Denmark, most belonging to TETTIGONIIDAE, including
two large green Tettigonia species and the spotted-winged Decticus verrucivorus [vortebideren];
probably the most frequently observed species is the smaller Meconema thalassinum
[egegræshoppen]. GRYLLIDAE ('fårekyllinger") are represented in our fauna by the introduced
Acheta domestica [husfårekyllingen], (Gryllus campestris ([markfårekyllingen] is known from
28
Bornholm, but has not been found here for many years now) and GRYLLOTALPIDAE by Gryllotalpa [jordkrebs].
Denmark is home to about 20 caeliferans; most belong to ACRIDIDAE, three to TETRIGIDAE
[torngræshopper].
Ole Fogh Nielsen’s De Danske Græshopper (Apollo Books, 2000) is an information-packed and
superbly illustrated account of our orthopterans.
DICTYOPTERA s.lat. cockroaches [kakerlakker], termites [termitter], mantids [knælere];
treated in SAE as 3 distinct 'orders' Blattodea, Isoptera, Mantodea SAE 125, 266-283
As noted SAE p. 125 the interrelationships between the three phenetically quite distinctive
dictyopteran groups remain debatable, but the bulk of the presently available evidence supports that
the cockroaches are indeed paraphyletic in terms of the termites – and the composite group is, then,
the sister group of the mantids (Deitz et al. Ent. Abhandlungen 61: 69-91, 2003).
The Australian Mastotermes darwiniensis is unique among termites in having retained a distinct
hind wing vannus (SAE fig. 20.1E) and all 5 tarsomeres. It is most likely the sister group of all
other extant termites. This time-honoured view has been challenged in the early 1990s, but is
supported in a more recent analysis of termite phylogeny based on a sizable morphological data set
(Donovan et al., 2000, Biol. J. Linn. Soc. 70: 467-513).
In N. Europe only cockroaches are represented; 3 species of Ectobius occur in nature, all others
(less than a dozed regularly occurring) are introduced.
PHASMATODEA, stick and leaf insects [vandrende pinde og blade] SAE 126, 297-301
Do note that the elongation of the meso- og metathorax are not phasmatodean ground plan
specializations of the order: its most basal extant members (the N. American Timema, Fig.16.C)
have ordinary body proportions. The order is un-represented in N.Europe.
Mapping the presence/absence of wings on a recent phylogeny of the Phasmatodea led to the
conclusion that wings were absent in the ordinal ground plan (Whiting et al. Nature, 421: 264-267,
2003).the presence of wings in subordinate lineages must accordingly be interpreted as a character
reversal.
EMBIOPTERA (EMBIIDINA), webspinners SAE 126, 302-305
The order is un-represented in N. Europe, but a few species occur in the Mediterranean
GRYLLOBLATTODEA (=NOTOPTERA), ice (or rock) crawlers SAE 125, 284-285
The order is un-represented in Europe.
MANTOPHASMATODEA, heel-walkers (unmentioned in SAE)
The discovery of the Mantophasmatodea in 2002 (Klass et al., Science 296: 1456-1459) was a
source of some excitement in the entomologists’ community; the last finding of an insect that
clearly proved un-assignable to a recognized ‘order’ was in 1914 (Grylloblatta).
Adult mantophasmatodeans (Fig.16D) are about 2 cm long and completely apterous. Females are
immediately separable from generalized stick-insects by the lack of a venter VIII ‘operculum’:
concealing the base of the short ovipositor (Fig. 16F), and both sexes by the absence of defensive
glands discharging on the pronotal fore corners. The pronotal margins are not produced posteriorly
and laterally, hence unlike in orthopterans there is no prothoracic ‘cryptopleury’. The cerci are stout
and unsegmented, strongly curved in males. The male sternum IX bears a posteromedial process
(Fig. 16E). All five tarsal segments are discernible, though the basal three are synscleritous; the
arolium is very large. The proventricular section of the fore gut has a cuticular armature strongly
29
reminiscent of that in Grylloblattodea. As noted above a sister-group relationship between the two
orders is also supported by recent molecular evidence.
About a dozen species are currently named. All so far recorded extant taxa are from the
Afrotropics, most are from S. Africa/Namibia, but one single specimen of a distinct species is from
Tanzania. However, a Baltic amber (Eocene) fossil insect almost certainly also belongs to this
order, which, then, previously must have had a more extensive range.
Mantophasmatodeans are nocturnal carnivores, catching small arthropods with their somewhat
spiny fore-and middle legs. They owe their vernacular name to their habit of lifting the tarsal apex
from the substrate (the alternative vernacular name ‘gladiator’ appropriate applies only to a few
spiny-bodied species).
PLECOPTERA, stoneflies [slørvinger] SAE 124-125, 263-265
The nymphs of our Plecoptera can be immediately distinguished from those of mayflies [døgnfluer]
by their lack of the median terminal filament. A short filament does occur in some non-European
stonefly nymphs (and nowehere else among extant neopteran insects), but is perhaps an
autapomorphic neoformation rather than a plesiomorphy.
Adult stoneflies eat lichens or algae, or they do not feed at all.
25 species have been found in Denmark, but some of these are believed now to have become
extinct here during the 20th century (running-water animals are vulnerable!); this may be true, e.g.,
of the largest species recorded from the country, Dinocras cephalotes.
ZORAPTERA SAE 127, 306-307
The bionomics of the group is overall poorly known, and so is its morphology and its phylogenetic
affinities. Zorapterans are one of the great challenges of present-day systematic entomology!
Tropical, including part of the USA; absent from the Palaearctic region and Australia.
DERMAPTERA, earwigs [ørentviste] SAE 126, 286-289
5 species occur in Denmark, Forficula auricularia being by far the most common and familiar; in
spite of its well-developed hind wings it extremely rarely flies.
PSOCODEA: Psocoptera+Phthiraptera SAE 127-128, 308-315
Probably the most important synapomorphy of "Psocoptera" and Phthiraptera is a complement of
peculiar sclerotizations on the hypopharynx, shown here in Fig.17A: Paired ovoid ’lingual sclerites’
are connected to the socalled ’sitophore’ sclerotization (on the hypopharyngeal base) by narrow
sclerotized grooves (here foming an inverted Y). This is known to be a device for water-uptake: a
hygroscopical film of saliva (i.e., a secretion from the labial glands) may cover the lingual sclerites
and here absorb water from the atmosphere; the cavity in the centre of the sitophore fits a knob on
the ceiling of the preoral cavity, and when this knob is lifted (by contraction of the sucking pump
dilators originating on the clypeus on the anterior surface of the cranium) the resultant vacuum
draws fluid from the lingual sclerites through the delicate sclerite grooves.
There is now good evidence that the ’Psocoptera’ are indeed paraphyletic in terms of the parasitic
lice. This certainly makes sense from an evolutionary-ecological perspective. Note, for instance,
that loss of wings is characteristic of some ’psocopterns’, and also that a number of these live in
nests of mammals and birds.
PTHIRAPTERA (lice in the broad sense) comprise 4 lineages:
1) AMBLYCERA, characterized by rather short, clavate antennae which are concealed in a
groove on the lower surface of the head capsule. Comprise both mammal and bird parasites.
Habitus SAE fig. 29.1I.
30
2) ISCHNOCERA. The antennae are not clavate (but some segments may bear, often sexually
domorphic, processes) and are somewhat longer than those of the Amblycera. The mouthparts are
downwards-directed. Likewise comprise both mammal and bird parasites.
3) RHYNCHOPHTHIRINA. Just one genus Haematomyzus. Head capsule (Fig. 17B) produced
into a snout with apically situated mandibles. The latter can perform outwards directed movements
(and their abductors are more powerful than the adductors) and anchor the louse in the host skin.
The best known species H. elephantis on elephants (both African and Indian!), the two other on
African pigs (warthog and bush-pig, respectively).
4) ANOPLURA (= Siphunculata’, sucking lice) are characterized by strongly modified mouth
parts. SAE mentions the presence of three stylets in the anopluran mouth apparatus, but this is an
oft-repeated error based on preparation artefact; there are actually only two (Fig. 17C). The
anterior/dorsal stylet (largely formed by the hypopharynx) has on its posterior/loswer wall a tubular
sector, which serves the outlet of saliva; during the preparation of histological sections this sector
usually becomes disassociated from the other part of the stylet. The host blood is sucked up through
the concave dorsal surface of the anterior stylet. Derivatives of both the mandibles and maxillae are
recognizable in the base of the moth apparatus (Ramcke: Zool. Jb. Anat. 82: 547-663, 1965).
About 30 species free-living psocodeans (i.e., ‘psocopterans’) are known from Denmark, and a
somewhat higher number of the parasitic forms, but neither has been the subjected to long-term
targeted investigations. The study of the Danish fauna of parasitic lice is an excellent subject for
‘hobby-research’ for biologists – particularly for those who take an active interest in entomology as
well as birds/mammals!!!
THYSANOPTERA [blærefødder, thrips] SAE 128, 330-333
As noted in SAE the females of some taxa have retained a rather typical ovipositor, while in the
majority of the thysanopterans it is lost. This was the basis for the conventional subdivision of the
two suborders TEREBRANTIA and TUBULIFERA, but the monophyly of the Terebrantia can, of
course, not be upheld on the basis of this plesiomorphic character state.
Less than 100 species of thrips have so far been recorded from but the total number present here
may be around 150.
HEMIPTERA [næbmundede] SAE 128, 316-329
The morphological interpretation of the stylets pertaining to the mandibular as well as the maxillary
appendages is controversial; the same is true for the plate-like folds from the head capsule which
conceal the stylet bases; stylet protrusion is illustrated in Fig. 17D. Particularly noteworthy details
in the internal anatomy include the telotrophic (=acrotrophic) ovarioles (Fig. 17E) and the ‘filterchambers’ which have been independently evolved on more occasions in plan-sucking lineages
(‘short-circuits’ between the fore-and hind end of the midgut, serving rapid elimination of water
from the ‘thin solutions’ of nutrients, see Fig.17F)
The Hemipter are in SAE grouped into 4 ‘suborders’22:
1) STERNORRHYNCHA. A striking autapomorphy is the stongly backwards flexed head
capsule: the proboscis seemingly originates between the forelegs. The wing venation is always more
or less simplified. The are four main lineages; all are cosmopolitan and their members are plantsuckers:
22
A taxon ’Homoptera’ comprising the non-Heteroptera was abandoned by phylogenetic systematists some 30 years
ago (it is based on its members’ usually un-specialized forewings, hence a plesiomorphy) but is still retained in several
general texts.
31
PSYLLOIDEA, jumping plant lice, [bladlopper]. Superficially similar to small plant- or
leafhoppers, but the forewing venation is characteristic: a ’tree’ with a single stem. About 50
species in Denmark.
ALEYRODOIDEA, mealy bugs [mellus]. Body and wings whitish due to a ’powder’ of wax
particles. Wing venation extremely reduceded (SAE fig. 30.4D). Only few species are known from
Denmark, where the group has not been subject to targeted study.
APHIDOIDEA, aphids [bladlus] is a truly successful group in the northern temperate regions (in N.
Europe about as species-rich as the Heteroptera), but it is poorly represented in the tropics and the
temperate regions of the S. Hemisphere. APHIDIDAE s.str. i.e., the aphids that have siphunculi
[rygrør] (paired tubular structures on abdominal segment V, visible as short, stout cone-like
formations in SAE fig.30.10, but often much more prominent; they give off alarm pheromones) and
whose parthenogenetic females are viviparous, are by some authors treated as a superfamily with
several families; they comprise the vast majority of out aphids. The family ADELGIDAE (that fomr
ananas galls [ananasgaller] on conifers) are more generalized than other aphidoids in having
retained an ovipositor. Many aphids have great economic importance through damage caused by
their sucking and by their transmission of lant diseases.
COCCOIDEA, scale insects [skjoldlus] are, on a global scale somewhat more species rich than the
aphids, and their representation in the tropics is much more larger. Less than 100 species are known
from Denmark. The N. European scale insect fauna is another obvious subject for ‘hobby
research!’! Like the aphids the coccoids have many members that are of economical importance.
2) 'AUCHENORRHYNCHA' [cikader23]. Putative auchenorrhynchan autapomorphies include
the antennal structure (flagellum reduced, a bristle-like formation) and the sound-producing
apparatus (paired specialized regions in the lateral body wall in the abdominal base are drawn
inwards through the contraction of powerful muscles, and they ‘return’ due to elasticity). All
‘auchenorrhynchans’ are plant suckers. Two principal clades are recognizable, FULGOROMORPHA and CICADOMORPHA. Important families in the former are DELPHACIDAE
(planthopppers, with a prominent ’spur’ on the hind tibia), and FULGORIDAE (with the large
’lantern flies’ in S. America, famous for the enlarged and bizarrely shaped head capsule; not
represented in N. Europe). Important cicadomorphan families include CICADIDAE ([sangcikader],
not in Denmark; only males ‘sing’, but these are the only ‘auchenorrhynchans’ whose sounds are
audible to the unaided human ear, CERCOPIDAE ( froghoppers [skumcikader], with a few species
in N. Europe, some of which may be extremely abundant) and CICADELLIDAE (lefhoppers; in
N.Europe one of the most dominant insect groups in herbaceous vegetation. Delphacidae and
Cicadellidae both include serious agricultural pests. Ca 300 species of ’auchenorrhynchans’ are
known from Denmark.
In recent years the monophyly of Auchenorrhyncha has been questioned, because details in the
wing and male genitalia structure of Fulgoromorpha can be interpreted as indicating a sister-group
relationship to Coleorrhyncha+Heteroptera; the proposal has subsequently been supported also by
molecular evidence (e.g.,. Campbell et al., Syst.Ent. 20: 175-194, 1995). If it is indeed correct, the
specialised antennal morphology and the sound producing organs must have been evolved
independently in fulgoromorphans and cicadomorphans.
3) COLEORRHYNCHA. A single family, PELORIDIIDAE, with circum-antarctic range (austral
S.America., Australa, New Zealand etc.); ca 30 species. Plant suckers, all living in moist
bryophytes. Small, flattened insects (SAE fig. 30.11A) with a broad head capsule and horizontal
23
Til danskerne/For the Danes: "Cikader" bruges på dansk for ALLE 'auchenorrhyncher', iøvrigt ligesom 'Zikaden' på
tysk; men engelsk har IKKE nogen fællesbetegnelse for disse dyr: en 'cicada' er kun en sangcikade.
32
pronotal folds; fore wings thickened, with coarse venation, hind wings most often reduced, but fully
winged specimens do occur in some species.
4) HETEROPTERA, ’true’ bugs [tæger24]. While the most species rich subgroups are plant
suckers the most generalized lineages are carnivorous, and this life-style is usually presumed to be
ancestral within the Heteroptera. The ‘proboscis’ base is forwards directed (but the proboscis itself
is bent in repose, so that its apex is pointing backwards) and related to this modification the head
capsule is posteriorly (topographically ventrally) closed by a sclerotization. Another autapomorphy
is a well developed system of metathoracic stink glands in the adult (nympgs have another gland
complement in the abdominal dorsum). In contrast, the characteristic ‘hemelytra’ [halvdækvinger]
are presumably not an autapomorphy of the Heteroptera as a whole. There are about 500 species of
Heteroptera in Denmark.
The true bugs are classified into several ’infraorders’, the interrelationships of which have been
debated. It is likely that the
ENICOCEPHALOMORPHA (small tropical/subtropiscal-cosmopolitan group) and the
GERROMORPHA (cosmopolitan, the ’semiaquatic’ bugs) are the most basal lineages: they do
not have the specialized ‘hemelytra’ and this is presumably a genuine plesiomorphy. Among the
semiaquatic bugs (eight families, half of them represented in Denmark) adaptations for movements
on the free water surface has been evolved independently on more occasions; in the large family
GERRIDAE, water striders [skøjteløbertæger] the genus Halobates includes half a dozen species
adapted for life on the open oceans!
NEPOMORPHA are the water bugs [vandtæger] in the strict sense. They include the
CORIXIDAE [bugsvømmere], NAUCORIDAE such as Naucoris [rygsvømmerne], Ilyocoris
[vandrøveren ] and the wingless plastron-bearing Aphelocheirus [vandvæggelus] and the NEPIDAE
including, e.g. Nepa [skorpiontæge] and Ranatra [stavtæge].
CIMICOMORPHA and PENTATOMORPHA comprise the bulk of the true bugs.
CIMICOMORPHA include a number of carnivore lineages, of which we in Denmark have
representatives of, i.a., ANTHOCORIDAE, CIMICIDAE (bed bugs [væggelus], bldod sucking on
bats, birds – and humans), NABIDAE and REDUVIIDAE; the last mentioned include, e.g., the
harmless Reduvius personata [støvtæge] and the important experimental insect Rhodnius prolixus
(of S.American origin), which, with other members of the family, are important disease vectors.
Plant sucking cimicomorphans include TINGIDAE [masketæger] and theparticularly large family
MIRIDAE [blomstertæger] comprising ca. 2/3 of our native heteropterans. The
PENTATOMORPHA include plant suckers in the family LYGAEIDAE [frøtæger] and the wellknown PENTATOMIDAE [bredtæger/stinktæger].
Superorder ENDOPTERYGOTA [inskter med fuldstændig forvandling] SAE 128 ff
The Endopterygota comprise more than 80% of all insects. Their principal synapomorphy is the
unique larva whose eyes (almost always small groups of simple eyes, ’stemmata’) are broken down
at metamorphosis, and whose rudiments of wings and external genitalia are located in epidermal
pockets below the cuticle, SAE fig. 2.55B. The final immature stage is termed the pupa. It is
comparable to the final immature instar of non-endopterygotes, but is specialized in always being
inactive, non-feeding; they are very often enclosed in a pupal shelter or coccoon, usually spun from
24
Til danskerne/For the Danes: Navnet "tæger" bruges stadig i vide kredse om flåter, altså midefamilien Ixodidae. Det
har utvivlsomt også været den oprindelige hovedbetydning af ordet: flåter hedder ticks på engelsk og Zecken på tysk. Men
på norsk har tæge-navnet været brugt om de - ligeledes blodsugende - heteropterer Cimex (som vi nu kalder væggelus), og
det er tilsyneladende herfra, navnet blev indført for insektgruppen i 'officielt' dansk zoologsprog omkring 1770.
33
silk secreted by the larva. The pharate adult, i.e., the adult insect that is still enclosed in the pupal
skin (which it may be for some time), may move very actively after escaping from the pupal
chamber. Pupae that have movable mandibles useable for opening the chamber are referred to as
decticous (if they are not, they are said to be adecticous).
It must be emphasized that the more or less profound metamorphosis in some subordinate
paraneopteran groups (SAE 325, 331) are a morphological/physiological parallelism of endopterygote metamorphosis, not a phylogenetical forerunner of the latter.
The endopterygote phylogeny in Fig. 18 here shows the principl groupings within the individual
‘orders’. It is more updated than SAE p.125, fig 5.5, but some details are debatable.
As mentioned below the placement of the Strepsiptera within the Endopterygota has been
questioned, but the monophyly of the group otherwise appears well supported.
STREPSIPTERA [viftevinger] SAE 128, 360-364
In the most primitive extant Strepsiptera the females are apterous, but they do have legs and
compound eyes, and they are free-living (SAE fig. 36.2A), as is the final larval instar. They pertain
to the small family MENGENILLIDAE (Mediterranean, China, Australia) and they parasitize
zygentomans.
As mentioned SAE 128 some Strepsiptera have pharate late juvenile stages with external wing
rudiments. Moreover, the larval eyes reportedly are taken over unchanged by the adults. These facts
are the basis why the placement of the group within the Endopterygota has been questioned. It
remains debated, however, whether the external wing rudiments are indeed a strepsipteran ground
plan feature. If the Strepsiptera are indeed endopterygotes, a sister group relationship to the beetles
is a possibility: possible synapomorphies are the flight mechanism (’posteromotorism’, i.e., only the
hind wings are true organs of flight) and the large size of the thoracic sterna (which are larger than
the terga). Putative beetle/strepsipteran synapomorphies in the structure of the wings and wing base
(Kukalová-Peck & Lawrence 1993, Canad.Ent. 125: 181-258) were rejected byWhiting &
Kathirithamby (1995, J.N.Y.ent.Soc. 103: 1-14), but this controversy remains unfinished (KukalováPeck, pp. 249-268 in Fortey & Thomas eds Arthropod Relationships, Chapman & Hall 1997).
A radical innovation of the discussion about strepsipteran relationships is the proposal by Whiting,
Wheeler and their coworkers (1994, Nature 368: 696; more detailed accounts Syst. Biol. 46: 1-68,
1997 & Cladistics 17: 113-169, 2001) that they are the sister group of the Diptera. This proposal is
based on similarities in 18S og 28S rDNA, but morphological arguments are also provided, and –
most remarkably – an argument from developmental genetics: the strepsipteran thorax is derived
from a Dipteran-type thorax through a 'homeotic mutation' which has interchanged meso- og
metathorax! The strength of both the molecular and the morphological evidence remains debated
(Kristensen Eur. J. Entomol. 96: 237-253, 1999, and references therein).
The strepsipteran fauna of Denmark remains largely unstudied; only a couple of species (in the
planthopper/bee/wasp parasitizing taxa) have been recorded from the country.
NEUROPTERIDA [netvinger s.lat.] SAE 129, 334-344
RAPHIDIOPTERA, snakeflies [kamelhalsfluer] and MEGALOPTERA, are both small orders,
each with a couple of hundres species. The former is a purely northern-hemisphere group (2-3
species in Denmark) and is extremely homogeneous. The latter comprises the family SIALIDAE
[dovenfluer] with 3 species in Denmark, and the CORYDALIDAE (including, i.a., the large
American ’dobson flies’). The sister group relationship between raphidiopterans and megalopterans
(indicated in Fig. 18) is now questioned (see Aspöck et al. Systematic Entomology 26: 73-86, 2001;
Ent. Abhandlungen 61: 157-158, 2004; Haring & Aspöck Systematic Entomology 29: 415-430,
34
2004): the proposal has been made that the Neuroptera are the closest relatives of the Megaloptera,
and that the aquatic life-style is primitive also in the former. The problem arguably remains open. In
another very recent molecular (18S rDNA) analysis the Megaloptera come out paraphyletic in terms
of the other Neuropterida (Winterton, Ent. Abhandlungen 61: 158-160, 2004).
NEUROPTERA s.str. (= Planipennia) are represented in Denmark by 6 families with altogether
>50 species, most of them in the families CHRYSOPIDAE [guldøjer] and HEMEROBIIDAE
[florvinger]; our 3 species of MYMELEONTIDAE [myreløver] all have very restricted ranges.
COLEOPTERA, beetles [biller] SAE 129, 130, 345-359
Comprises about one fourth of all described organisms, but in N. Europe it is surpassed – by far –
by flies as well as wasps. The composition of the Danish beetle fauna must be considered very well
known. An annual updating of the excellent Danish beetle catalogue from 1996 (M.Hansen ed.)
now shows now >3.700 species in DK.
Four beetle suborders are currently recognized: two very small ones, the moderately large
ADEPHAGA and the enormous POLYPHAGA. Their mutual relationships have been much
debated. A recent analysis pf an extensive morphological data set (Beutel, R. & Haas, F. 2001)
supports the phylogeny Archostemata + (Adephaga + (Myxophaga + Polyphaga)). The nonarchostematans ('Pantophaga') are characterized by simplifications in the thoracic skeleton and
musculature; the Myxophaga and Polyphaga share a specialized larval leg (only two segments
distad from femur, consistently unpaired claws). The non-polyphagan beetles share a characteristic
hind wing venation, with a so-called "oblongum", an elongate/ovoid oblique cell which at both ends
is closed by what is interpreted as a M-Cu crossvein, SAE fig. 35.3D-E; moreover, there is a hinge
on vein Cu just proximad from the oblongum. These venational characteristics are presumably
plesiomorphic at the coleopteran level.
ARCHOSTEMATA. Un-represented in N. Europe. Best known family CUPEDIDAE (about 20
species), characterized by peculiarly pitted and scaly elytra, which sometimes are interpreted as
plesiomorphic (derived from a wing with a fine-meshed reticulate venation; similar wings are
known from Permian deposits. The larvae live in rotten wood. Two additional, very small families.
MYXOPHAGA. Four species-poor families comprising tiny beetles that live in fresh water or
moist soil. Algal feeders. In Denmark represented by Microsporus acaroides (family
Microsporidae).
ADEPHAGA. Autapomorphies are a firm connection between the pronotum and the propleuron,
as well as a fsion of the hind coxae with the metasternum and the 2nd abdominal sternum (sternum I
is completely reduced), which they thereby ‘divide’, SAE fig. 35.4A. The suborder comprises about
one-tenth of all beetles, globally as well as in N. Europe. Several families of adephagans are often
recognized, but it is most likely that the large family CARABIDAE, ground beetles [løbebiller] as
usually delimited are paraphyletic in terms of many of the other.
In N. Europe the aquatic adephagans are represented by the GYRINIDAE, whirligig beetles
[hvirvlere], HALIPLIDAE, NOTERIDAE and DYTISCIDAE [egl. vandkalve] which were
previously collectively talked of as 'Hydradephaga', but they are not a monophylum. The Adephaga
are now believed to have invaded fresh water 3-4 times independently. CARABIDAE in the strict
sense comprise the 'typical’ ground beetles (ca. 300 speces in Denmark), autapomorhic groups like
the CICINDELINAE , tiger beetles [sandspringere] with 4 species in Denmark and PAUSSINAE
(exotic; myrmecophilse that feed ants by secretions given off from, i.a., the thickened antennae).
Most are carnivorous both as larvae and well as adults, but herbivores do occur.
POLYPHAGA. Autapomorphies of this enormous group include, i.a., the prothoracic
’cryptopleuron’ (the pleuron, which is fused to the trochantin, is covered by the pronotum) and the
telotrophic (=acrotrophic) ovarioles (parallelism to Hemiptera and some Neuropterida!). The
35
classification of the Polyphaga is very difficult; one recognizes some 20 superfamilies grouped into
‘series’. Only few of these higher taxa have easily recognizable autapomorphies. Some important
taxa are: HYDROPHILOIDEA including, e.g. HYDROHILIDAE [vandkærer].
STAPHYLINOIDEA with, e.g. SILPHIDAE [ådselsbiller] and the STAPHYLINIDAE [rovbiller],
with usually short elytra and the hind wings complexly packed below the latter; in N. Europe this is
the most species-rich animal family (>900 species in Denmark). SCARABAEOIDEA [torbister]
with characteristically lamellate antennal apices include LUCANIDAE [hjortebiller; ‘eghjorten’
Lucanus cervus the largest native beetle in Denmark, believed to be extinct here since the mid-20th
century), GEOTRUPIDAE [skarnbasser] and SCARABAEIDAE [gødningbiller, oldenborrer,
guldbasser, næsehornbiller m.m.]. BYRRHOIDEA include terrestrial taxa as well as families with
aquatic members such as ELMIDAE (with plastron respiration, SAE 33 and fig. 2.14) in adults.
ELATEROIDEA including, i.a., ELATERIDAE [smældere], CANTHARIDAE ([blødvinger]; the
adults are among the most conspicuous diurnal beetles in N. Europe, on flowers and foliage) and
LAMPYRIDAE [Sankt Hansorme] with luminescent organs in adults as well as larvae, females
wingless. BOSTRICHOIDEA include serious household pests in the families DERMESTIDAE
[klannere] and ANOBIIDAE [borebiller & tyvebiller]. CUCUJOIDEA include NITIDULIDAE
[glimmerbøsser] and COCCINELLIDAE (ladybird beetles [mariehøns]). TENEBRIONOIDEA are
the 'heteromerous' beetles; the name alludes to the fact that the tarsi have different segment
numbers: fore- and mid-tarsi have 5, hind segments 4; they include, e.g., the TENEBRIONIDAE
[skyggebiller], MELOIDAE [oliebiller m.m.] and PYROCHROIDAE [kardinalbiller].
CHRYSOMELOIDEA and CURCULIONOIDEA constitute an immensely successful lineage,
almost exclusively comprising herbivorous members. A possible synapomorphy is the
‘kryptopentamerous' tarsi (SAE fig.35.8D): the 4th tarsomere is tiny and seen from below it is
completely concealed by the large bilobed 3rd tarsomere. The former include the
CERAMBYCIDAE (longhorn beetles [træbukke]] and the CHRYSOMELIDAE (leaf beetles
[bladbiller]], the latter (weevils [snudebiller]) a suite of families of which CURCULIONIDAE
(with about 50.000 known species) is the largest family in the Animal Kingdom; the bark
beetles[barkbillerne] SCOLYTINAE, are now considered a subordinate curculionid lineage.
HYMENOPTERA [årevingede, hvepse] SAE 130, 132, 406-418.
One of the largest insect orders. At least in N. Europe it is the largest, with >7000 species
The retention in the Hymenoptera of an ovipositor with all typical elements is a unique
plesiomorphy at the endopterygote level (cp. SAE fig. 5.6 and 42.4A-B).
The SAE systematic account has two hymenopteran ‘suborders’: ‘Symphyta’ (sawflies) and
Apocrita (waist-wasps). The former ['plantehvepsene'/'blad- og træhvepse'] is clearly paraphyletic in
terms of the latter. Among its members may be mentioned the XYELIDAE, a small family which in
some characters is more primitive than any other Hymenoptera (the fore wing has a forked Rs and
the pupa has movable mandibles – hence it is untrue that hymenopteran pupae are consistently
adecticous, as stated SAE 412); it is represented in Denmark by Xyela julii. Moreover
TENTHREDINIDAE (comprising the majority of our non-apocritans), CIMBICIDAE (large, robust
insects with clubbed antennae), and SIRICIDAE [træhvepse] with wood-boring larvae. ‘Typical’
free-living sawfly larvae (SAE fig 42.5A) are superficially similar to ‘typical’ lepidopteran
caterpillars, but have more pairs of abdominal prolegs (on abdominal segments II-VIII, X,
lepidopterans only on III-VI, X), and these have never crochets; moreover, the larval eyes on each
side form a small compact group covered by a common corneal lens (lepidopteran caterpillars
usually have 6 separate simple eyes on each side. The sister group of the Apocrita is the family
ORUSSIDAE, whose larvae in contrast to those of other ‘symphytans’ are not herbivores but
36
parasitoids - on larvae of wood-boring beetles and siricids. This beautifully fits the scenario one
would a priori propose for the origin of the Apocrita. It is a small family (< 100 species) whose
members are rarely observed; none of the European species are recorded from Denmark.
The monophyly of the APOCRITA [stilkhvepsene] is convincingly supported by the petiole
[hvepsetaille] (SAE 410-411), and by the larval midgut being non-continuous with the hindgut; the
larvae are consistently legless.
The overwhelming majority of the apocritans, and hence of the hymenopterans (by us ca 5/6 of the
members of the order) have larvae that are parasites (or better: 'parasitoids', because the hosts are
almost always killed) in other insects. The predominately parasitoid families are often talked of
collectively as the 'Parasitica' [snyltehvepse], but this assemblage is almost certainly not a
monophylum. It includes a suite of superfamilies including the'megadiverse' ICHNEUMONOIDEA
(small to middle-sized, very rarely large insects; larvae usually parasitoids in insect larvae) and
CHALCIDOIDEA (small to tiny insects, larvae often parasitoids in insect eggs). The latter also
does comprise herbivorous members, and so does the superfamily CYNIPOIDEA, which include
gall-formers [galhvepse]. The representation of the 'Parasitica’-families in Denmark is overall very
poorly known – excellent topics for biologists’ ‘hobby-research’!
The taxa which in SAE are talked of as the superfamilies CHRYSIDOIDEA, VESPOIDEA,
SPHECOIDEA and APOIDEA together constitute the clade ACULEATA, characterized by
apomorphic details in the structure of the ovipositor, and not least its function: it only works as a
‘sting’ [giftbrod], and no longer plays any role in ovipositon (the female gonopore is located in
front of the ovipositor base).
CHRYSIDOIDEA including, i.a., CHRYSIDIDAE [guldhvepse] (often predators on larvae of
solitary bees and wasps) and DRYINIDAE (parasitoids of leaf- and planthoppers) are perhaps the
sister-group of the remaining Apocrita; unlike in the latter the sting apparatus is not completely
concealed within abdominal segment VII.
VESPOIDEA including, i.a., MUTILLIDAE [fløjlsmyrer] (females wingless, larvae mostly
predators on larvae of other aculeate Hymenoptera), POMPILIDAE [vejhvepse] (larvae in
chambers in soil, provisioned with spiders), SCOLIIDAE, (ectoparasites on coleopteran larvae, in
the tropics including some of the largest hymenopterans), VESPIDAE [gedehamse] (characterized
by the capacity of folding their wings longitudinally, include both solitary and social taxa) and
FORMICIDAE, ants [myrer] (all social, about 50 species in Denmark).
APIDAE s.lat. (SAE: overfam. APOIDEA), the bees, are apparently cladistically subordinate in
the SPHECOIDEA/SPHECIDAE, digger wasps [gravehvepse]; the ground plan autapomorphies of
the APIDAE are the body ‘fur’ (secondarily lost in non-pollen-gatherers) and the broad, flat
proximal tarsus segment on the hind legs. There are about 120 species of digger wasps in Denmark,
and probably about twice as many bees (a modern check-list is highly desirable!).
True sociality has been evolved >10 times independently within the Hymenoptera-Aculeata, and
only very few times elsewhere in the animal kingdom (among insects notably termites and some
Thysanoptera). It has been pointed out, that the special sex determination mode of Hymenoptera,
haplodiploidy25, may have favoured evolution of sociality because female hymenopterans share
more genes with their sisters [(1 x ½) + (½ x ½) = ¾ - if the mother has mated just once] than with
their own offspring (½).
A special issue of Zoologica Scripta 28(1-2) 1999 brings a lot of pertinent information on
Hymenoptera evolution.
MECOPTERIDA ('panorpoid' groups)
25
For the Danes/til danskerne: med HAnlig HAploidi
37
The possible monophyly of Mecopterida + Hymenoptera (SAE 130) may apparently be supported
by the fact that adults in both groups have a completely sclsrotized plate in the floor of the sucking
pump. In the plesiomorphic condition there is just a sclerotized rod in each side of the pump; this
condition is retained in neuropterids and beetles (Kristensen, Eur. J. Entomol. 96: 237-253, 1999).
ANTLIOPHORA SAE 131-132
The close relationship between scorpion flies and fleas have in recent years been supported by
molecular data. It is even suggested, that the fleas may be just a subordinate group within the
scorpion flies. The putative morphological ground plan autapomorphies of the latter (SAE 132)
therefore need renewed scrutiny.
MECOPTERA, scorpion flies [skorpionfluer] SAE:132, 365-368
Scorpion flies are immediately separable from the neuropterids by their paucity of cross veins
behind the costal margins of the fore wings. The basal segment of the 2-segmented appendage
(’gonopod’) on the male abdominal segment IX is strongly swollen; the diameter of the
immediately preceding segments are in some families markedly tapering and upwards bent, and
these two specializations together account for the ’scorpion-tail’-like abdominal tip to which the
group owes its vernacular name. In contrast to other small endopterygote orders such as
Raphidioptera, Megaloptera and Strepsiptera the Mecoptera are strikingly diverse. Note that the
larvae have retained compound eyes (which, however, reportedly are broken down at metamophosis
and reconstructed de novo as in other endopterygotes) and, probably in the ground plan, also a
median ocellus; both conditions are unique plesiomorphies at the endopterygote level.
Of the 9 extant families the following shall be mentioned:
NANNOCHORISTIDAE (<10 species, circum-antarctic). The only mecopterns with aquatic
larvae; these are carnivorous and very different from other scorpion fly larvae (SAE fig. 37.3E-G).
Adult nannochoristids have some plesiomorphies in the structure of the genital segments, which set
them apart from other mecopterans; also the adult’s head capsule is, unlike that of other scorpion
flies, not pronouncedly produced into a ’snout’. The Nannochoristidae have, like the following
family and the fleas an ovariole type, which can be interpreted as being secondarily panoistic. Do
these groups together constitute a monophylum? (Simiczyjew, Acta Zoologica 83: 61-66, 2002).
BOREIDAE, snow fleas [snelopper] have reduced wings as adults. Moss-feeders, one species in
Denmark. This is the family which in some molecular analyses come out as the sister group of the
fleas. BITTACIDAE are mostly large, long-legged insects. The adults are predators, the larvae (as
in most mecopterans) soil animals. Almost cosmopolitan, but absent from N. Europe.
PANORPIDAE include the majority of the scorpion flies; there are a few species in Denmark. The
adults are mostly scavengers, some being renowned for their ability of grasping dead insects from
spiders’ webs.
The families MEROPEIDAE (one species in N.Am. and one in Australia!) and EOMEROPEIDAE (=
NOTIOTHAUMIDAE, one species in S. America) have been subject to particular interest. These insects have broad
wings with a densely reticulate venation. This feature was long considered to be plesiomorphic, and the two families
were placed in a separate suborder ("Protomecoptera"). However, judging from the genital segments in both sexes the
two are not each closest relatives, and at least the Eomeropeidae apparently belong to a subordinate clade that comprises
neither the Nannochoristidae, the Boreidae and the Bittacidae. The wing morphology of the two families may therefore
be considered specialized – and independently so.
Many fossil insect wings from the Permian onwards have been assigned to the Mecoptera, but they
may as well belong to other lineages within the Mecopterida: the Mecoptera have no known ordinal
autapomorphies in the wing structure!
SIPHONAPTERA (lopper) SAE 132, 369-373
38
See above under Mecoptera. About 50 species are known from Denmark, but our native fauna of
these insects has only been sporadically studied.
DIPTERA [tovingede] SAE 132, 374-387
The Diptera have fewer described species than the Coleoptera and Lepidoptera; in N. Europe it is,
however, with >6000 species second only to Hymenoptera. And one would arguably describe it as
the most diverse of the large endopterygote orders.
What is called in SAE the hypopharynx in the dipteran mouth apparatus is actually a formation
peculiar to the order, the ‘lonchus’ [spytklingen], which, as shown by it containing the salivary
duct, is a morphologically composite formation comprising a hypopharyngeal and a prelabial
element.
Note. The Diptera classification in SAE is conservative, non-phylogenetic (Don Colless has been a
prominent proponent of phenetic systematics). Of the three ‘suborders’ recognized the 'Nematocera'
([myg]. With unspecialised antennae, SAE fig 39.1G-I – the name Nematocera means “threadhorn”), paraphyletic in terms of the BRACHYCERA [egl.fluer]. The arrangement of the
nematoceran assemblages in Fig.18 is very tentative and may prove incorrect.
The Brachycera are mostly more robuste than the nematocerans, the antennae are shortened and
the basal flagellomere often enlarged. However, in the ground plan of the Brachycera antennal
structure is still unspecialised. An important autapomorphy is a rotation of the larval mandibe plane
of movement: the anterior articulation lies mediad from the lateral, and the mandibles hence are no
longer moved toward each other, but in parallel planes.
The brachyceran group 'Orthorrhapha' is paraphyletic in terms of the CYCLORRHAPHA, whose
autapomorphies are the ‘typical fly antenna’ (SAE fig. 39.1J), the puparium and the ‘maggot’ larva
which is devoid of head capsule and has a complex mouth apparatus ('cephalopharyngeal-skeleton',
SAE fig. 39.6C). The morphological interpretation of the elements of the latter is controversial (in
SAE the ‘mouth hooks’ are considered mandibular, but judging from their ontogenetic development
they also include significant components from the maxillary segment). Finally it appears that the
'Aschiza' are paraphyletic in terms of the SCHIZOPHORA; the autapomorphy of the latter is the
ptilinum ['pandeblære' ] (SAE 374), which during eclosion is evaginated by blood pressure and
serves to open the ’lid’ of the puparium; after eclosion it is withdrawn (by means of a muscle) and
leaves a scar ['pandespalte'] above the antennae (visible as an inverted V in SAE fig. 39.1A).
Among the nematoceran families - in N.Europa comprising about 1/3 of the dipteran species – the
following should be mentioned: TIPULIDAE [stankelben], CULICIDAE [stikmyg],
CHIRONOMIDAE [dansemyg], CERATOPOGONIDAE [mitter], SIMULIIDAE [kvægmyg],
BIBIONIDAE [hårmyg] og MYCETOPHILIDAE [svampemyg]; the CECIDOMYIIDAE [galmyg]
with >600 N. European species is our largest dipteran family, and its representation in Denmark is
very poorly investigated.
Among the non –cyclorrhaphan brachyceran flies the following may be mentioned:
STRATIOMYIDAE [våbenfluer], TABANIDAE [klæger], RHAGIONIDAE [sneppefluer],
ASILIDAE [rovfluer], THEREVIDAE [stiletfluer], BOMBYLIIDAE [humlefluer], EMPIDIDAE
[dansefluer] and DOLICHOPODIDAE [styltefluer]; the two last-mentioned are apparently among
the closest relatives of the Cyclorrhapha.
Noteworthy among the very numerous families within the successful CYCLORRHAPHA are the
families SYRPHIDAE (hover flies [svirrefluer]) and PIPUNCULIDAE [øjefluer]; both are
'aschizans', hence devoid of a ptilinum. Moreover TEPHRITIDAE [båndfluer], AGROMYZIDAE
[minerfluer], DROSOPHILIDAE (fruit flies [bananfluer], including the celebrated Drosophila
melanogaster), BRAULIDAE [bilus], SCATHOPHAGIDAE [møgfluer], ANTHOMYIIDAE
[blomsterfluer], MUSCIDAE (with Musca domestica [stuefluen]), CALLIPHORIDAE [spyfluer],
39
SARCOPHAGIDAE [kødfluer], TACHINIDAE [snyltefluer], GASTEROPHILIDAE [bremser],
GLOSSINIDAE [tsetsefluer], and HIPPOBOSCIDAE [lusefluer].
The Danish fauna of Diptera is very unevenly investigated. Next to the parasitoid Hymenoptera
some dipteran families represent the most serious lacunae in the knowledge of our national insect
fauna. An interesting recent checklist recorded documented Danish occurrence of 4.361 species, but
estimated a total exceeding 5.850 (Petersen & Meier, Steenstrupia 26: 119-276, 2002).
AMPHIESMENOPTERA SAE 132
TRICHOPTERA [vårfluer] SAE 132, 388-394
The two large superfamilies recognized in the SAE system are apparently both monophyla:
INTEGRIPALPIA s.str. (= Dicloacia, = Limnephiloidea s.lat.). Larvae hypognathous, casebuilding. Include, e.g., the PHRYGAENIDAE (with the largest Danish caddisflies) and
LIMNEPHILIDAE (the most species-rich caddisfly family, globally and in Denmark).
ANNULIPALPIA (=CURVIPALPIA, = Hydropsychoidea s.lat.). Larvae prognathous, usually
net/retreat-spinning. Adults with the apical segment of the maxillary palp elongated and annulated.
In contrast, it remains uncertain how the remaining four overall generalized families should be
classified. Some consider them to constitute a monophylum, 'SPICIPALPIA' (SAE's
'RHYACOPHILOIDEA', but the assemblage is more likely paraphyletic in terms of one or both of
the large lineages. The four are RHYCOPHILIDAE (and its S-Hemisphere counterpart
HYDROBIOSIDAE; both have prognathous, free-living and carnivorous larvae),
GLOSSOSOMATIDAE (‘saddle-case’ makers) and HYDROPTILIDAE (the smallest caddisflies,
larvae initially free-living, later ‘purse-case’ makers).
A little less than 200 caddisfly species are known from Denmark.
LEPIDOPTERA [sommerfugle] SAE 132, 395-405
Note in Fig 18 that ca 98-99% of all Lepidoptera belong to the monophylum DITRYSIA,
characterized by a specialized female genital apparatus with separate openings for copulation and
oviposition (SAE 399 and fig. 41.5D; incidentally, fig. 41.5C is misleading, in as much as the
ductus bursae should originate from the ‘vagina’ dorsad from the ovaries, not ventrad from it, as
shown). The remaining assemblage of overall primitive lepidopterans comprises numerous speciespoor lineages, which have arisen in a sequence of evolutionary ‘splitting events’ in which one
‘typical lepidopteran apomorphy’ has been evolved after the other. The basal diversification mode
of the Lepidoptera is overall well understood – it has some similarity to that of the Hymenoptera
(with the Ditrysia being a counterpart of the Apocrita).
In the three most basal lineages (Fig. 18: ngl) the adults have retained primitive biting mouthparts.
MICROPTERIGIDAE [urmøl] (cosmopolitan, <200 known species, 7 in Denmark) as adults feed
on pollen or fern spores; the larvae are moisture-requiring ‘soil animals’ feeding on detritus, fungus
hyphae or liverworts [levermosser]. They are the only extant family of Lepidoptera in which nondependence on flowering plants may be the primitive condition. AGATHIPHAGIDAE (2 known
species, Australia, SW pacific) have larvae mining in seeds of kauri pin, Agathis; as many
endophytic larvae they are legless (SAE fig. 41.6G). Pupal mandibles hypertrophied (SAE fig.
41.6J). It is unknown whether the adults feed at all. HETEROBATHMIIDAE (9 known species,
temperate S.America) have larvae that are leaf miners in Nothofagus [sydbøge]; the adult moths
presumably feed on pollen in the same trees. This group shares some striking specializations
40
(including the prominent Y-shaped strengthening lines on the larval head capsule SAE fig. 41.6A:
'adfrontal suture') with the Glossata; these are presumably true synapomorphies.
All the remaining Lepidoptera belong in the monophyletic GLOSSATA, characterized by very
prominent ground plan autapomorphies. Most important are is the adult’s sucking proboscis formed
by the maxillary galeae (SAE 395, fig. 41,1A,B,F), while the mandible is reduced and only serves
the movement of the pupal mandibles for opening the pupal shelter. Also the larval spinneret (SAE
399 and fig. 41.6A) is a glossatan groundplan autapomorphy. The most basal glossatan grade is
represented by the ERIOCRANIIDAE, a small, purely Holarctic family (8 species in Denmark)
whose larvae are legless leaf miners in trees pertaining to the Fagales (mostly Betula and Quercus).
In the next ‘splitting events’ identifiable in the Recent fauna (some small non-European families)
additional specializations are acquired, including the hollow wing scales (SAE 396, fig. 41.4C,F)
and an intrinsic proboscis musculature, serving a firm coiling; even the short proboscis of the lowest
Glossata is coiled in repose, but that is due exclusively to the elasticity of the galea wall. The
NEOLEPIDOPTERA are characterized by important modifications in the immature stages: the
larvae acquire those crochet-bearing, musculated abdominal prolegs on III-VI og X (SAE figs
41.6B-D, F-I), that are so characteristic of most Lepidoptera caterpillars. The pupae become 'obtect'
[mumiepuppe] and 'adecticous' [ikke-bidende] ; hereby the adults’ mandibles completely loose any
role and become strongly reduced. The first differentiated Recent Neolepidoptera-group of lowerrank, EXOPORIA (represented in Denmark by HEPIALIDAE [rodædere]) have a strongly
autapomorphic female genital apparatus: as in the DITRYSIA (presumably convergently) there are
separate openings for copulation and oviposition, but the two systems have no internal connection;
after copulation the sperm travels in a gutter from the 'bursa' opening to the ovipore and thence to
the genital chamber/spermatheca.
The HETERONEURA are characterized by the fore-and hind wings having markedly different
venation: the hind wing Rs is unbranched. Moreover, the hind wings are by various means
(examples in SAE fig. 41.3D, D) coupled to the fore wings.
Roughly one-half of the ditrysians are overall small insects whose larvae live concealed (between
folded/spun leaves, or as leaf-, stem, fruit-miners) and have retained the primitive arrangement of
the proleg crochets (in circles). Together with the non-ditrysians these are collectively known as
'microlepidopterans' (or just ‘micros’) [småsommerfugle]. This assemblage include large
superfamilies as TINEOIDEA (with TINEIDAE [‘egl møl’] many of which feed on fungi, and some
on unusual substances such as keratin, hence they comprise some well known textile pests),
YPONOMEUTOIDEA, GELECHIOIDEA, TORTRICOIDEA [viklere], PYRALOIDEA (with
tympanic organs in the abdominal base) and small, but remarkable families like SESIIDAE
[glassværmere] of which many are wasp mimics, and PTEROPHORIDAE [fjermøl] whose mostly
deeply divided wings are a very unusual condition in the winged insects. ZYGAENOIDEAZYGAENIDAE [køllesværmere] have larval prolegs with crochets in ‘mesoseries’ ['klamrefødder']
see below; these are presumably evolved independently of those in the Macrolepidoptera.
The remaining ditrysians are termed Macrolepidoptera [storsommerfugle]. Their larvae are overall
more freely exposed, and the proleg crochets are arranged in a single median row (‘mesoseries’,
SAE fig. 41.6D). They may constitute a monophylum. Important lineages include the
HESPERIOIDEA+PAPILIONOIDEA, butterflies [dagsommerfugle]; BOMBYCOIDEA with
BOMBYCIDAE (the silkworm moth Bombyx mori), SATURNIIDAE [natpåfugleøjer] and
SPHINGIDAE, hawk moths [aftensværmere]; the latter includes the largest Danish Lepidoptera,
and indeed some of the largest Danish insects, in the genera Acherontia [dødninghoved], Agrius
[snerlesværmer] and Sphinx [ligustersværmer]. GEOMETROIDEA-GEOMETRIDAE [målere]
have a tympanic organ in the abdominal base, while the NOCTUOIDEA including the
NOCTUIDAE [ugler] have tympanic organs in the metathorax. ARCTIIDAE (tiger moths
41
[bjørnespindere]) and LYMANTRIIDAE [penselspindere] are perhaps just subordinate lineages
within the Noctuidae, which (even in a more restricted sense) is the largest family of Lepidoptera.
Tympanic organs have been evolved independently in several ditrysian lineages (not only those
mentioned above). They are known to register bat echolocation sounds, and it is likely that those
moth lineages whose ground plan comprises a well developed tympanic organ have evolved later
than the origin of the bats (around the Cretacous/Tertiary boundary??).
42
Figure captions
1 Summary cladogram of hexapods. The recently described Mantophasmatodea belong in the
'LOWER NEOPTERAN ORDERS' assemblage. From Kristensen in The Hierarchy of Life, Elsevier
1989.
2 A Head of generalized neopteran insect with hypothesized segmental limits indicated. 1
acron/ocular (protocerebral ) segment; 2 antennal (deutocerebral) segment; 3 intercalary
(tritocerebral) segment; 4 tetrocerebral segment (a highly reduced segment recognized in this
hypothesis, but not accepted by most authors), 5 mandibular segment; 6 maxillary segment; 7 labial
segment. C clypeus; F frons; L labrum; lb labium; md mandible; mx maxilla. From Chaudonneret
Cahiers d’Études Biologiques 13-15, 1964.
B Head of archaeognathan, near-horizontal section, anterior up; central nervous system hit both at
tritocerebrum (Tcr) and suboesophageal ganglion (MSOE). Note the two components of
non.cuticular ('ligamentous'/connective tissue) endoskeleton ltm and ltmx on which ventral muscles
of the manible (Md) and maxillary stipes (sti) originate. Anterior arm of cuticular tentorium
sectioned at TA. From Bitsch, Ann. Sci. nat. Zool. 11 S, 12, 1964.
C Head of generalized insect, some inner structures. b brain; cly clypeus; fg frontaal ganglion; hy
hypopharynx; oc ocellus; sd salivary duct; sg suboesophageal ganglion; te tentorium. Redrawn after
Snodgrass Principles of Insect Morphology, McGrawHill 1935.
D Head capsule of grasshopper, opened to show fully developed cuticular tentorium. Note anterior
tentorial arm (PT), anterior tentorial pit (pt), and 'corpotentorium' (tentorial bridge) (CT). From
Chaudonneret Bull. sci. Bourgogne 24, 1967.
3 A Antenna of insect, intrinsic musculature limited to scapo-pedicellar joint.
B Generalized antennal type, with muscles throughout the length.
C Section of antennal base of insect.
D Primitive (monocondylous) type of hexapod mandible as occurring in Archaeognatha.
E Generalized hexapod maxilla.
F Generalized hexapod labium
Redrawn from various sources, here from Kristensen Systematisk Entomologi Munksgaard 1970.
4 A-B. Kukalová-Peck's interpretation of the hexapod legs in a wing-bearing segment (A) and
abdominal segment (B) of a basal Palaeozoic pterygote insect, and a non-wing-bearing hexapod
thoracic segment (C). In addition to the usually recognized podomeres (leg segments) she
recognizes an epicoxa (ECX), subcoxa (SCX), prefemur (PFE), patella (PAT) and basitarsus (BT).
'Exite' branches originated just beyond the apical margin of a number of the basal segments; that
between the epicoxa and the subcoxa was allegedly particularly large (W) and it became the wing in
pterygote insects, while the subcoca is the sclerotized pleuron. The dorsal margin of the epicoxa is
contiguous with the tergum (TE) and this segment otherwise provided material for wing base
sclerites. In the abdomen all podomeres proximad from the 'prefemur' are hypothesized to have
become incorporated into the ventral 'sternal' plate. PRO in C is a 'protowing'. After Kukalová-Peck
Canad. J. Zool. 65, 1987.
C Kukalová-Peck's reconstruction of a Permian pterygote insect Uralia rodendorfi belonging to the
Palaeodictyopteroid 'order' Diaphanopterodea. Palaeodictyopteroids were 'palaeopterans'
characterized by sucking mouthparts, and the Diaphanopterodea.were unique within that
assemblage by having the capacity to fold their wings in a roof-like fashion over the abdomen parallelism to Neoptera? Note the exites on the thoracic legs, the subsegmented small abdominal
43
legs ("leglets") and the long, subsegmented and claw-bearing gonostylus (stylus on IX). Even the
maxillary and labial palps are interpreted as having borne paired claws! After Kukalová-Peck
Canad. J. Zool. 61, 1983.
5-6 Some inner organs of hexapods. Here from Kristensen Systematisk Entomologi Munksgaard
1970
7 Structural details of apterygote hexapods. D is a ventral view of a proturan head, showing the
'linea ventralis' (LV) - the apparently 'strong' synapomorphy between Collembola and Protura;
transverse sections of the 'linea' are shown to the left. After Francois Mem. Mus. nat. d'Hist. nat. NS
A, 59, 1969.
8. A A representative of the Palaeozoic apterygote taxon Cercopodata. After Kukalová-Peck Canad.
J. Zool. 65, 1987.
B. Early archaeognathan egg cleavage
9 A-I Dipluran morphology. Redrawn from various sources, here from Kristensen in Fortey &
Thomas (eds) Arthropod Relationships. London, Chapman & Hall, 1997.
J The Palaeozoic Testajapyx. After Kukalová-Peck Canad. J. Zool. 65, 1987.
10 A-B Symphypleonan Collembola, B during courtship (the male is the smaller individual). Here
from Kristensen Systematisk Entomologi Munksgaard 1970
C-F Entomobryomorph collembolan, with structural details Here after Kristensen Systematisk
Entomologi Munksgaard 1970
G Protura. Sketches of the living animals in natural posture with raised forelegs, from a
monumental monograph of the Protura published by the Italian entomologist A. Berlese two years
after the discovery of the group by his countryman F. Silvestri
11 Habitus (A) and several structural details (B-K) of archaeognathans - in many ways the starting
point for understanding the morphology of the Insecta. Note: Archaeognatha actually do not have an
‘epistomal sulcus’ (the line denoted “es” in B)!
12 Zygentoma.
A-B, lepismatids in dorsal (A) and ventral (B) view.
C a nicoletiid.
D-F, Tricholepidion, note the well developed compound eyes in E ; F is the ventral side of segment
VII; note the large sternal plate (S7) with similarly large coxopodites (Cx7), eversible vesicles
(EV) and styli (Sty).
G is the inner head skeleton of a lepismatid, note the fused anterior tentorial arms (AT, CT) which
are separate from the bridge (TB) formed by the fused posterior arms.
A-C after Watson in Insects of Australia, Melbourne University Press 1991. D,F after Wygodzinsky
Ann .ent. Soc. Amer 1961. E after Boudreaux Arthropod Phylogeny with Special Reference to
Insects Wiley 1979. G After Snodgrass A Textbook of Arthropod Anatomy Cornell Univ. Press.
1952.
13A, C-D Wing-bearing thorcic segments of generalized neopteran insects, B Base of extended
wing of same. For explanation of principal features see text pp. 23-24. After Snodgrass Principles
of Insect Morphology, McGrawHill 1935.
44
14 Transverse sections of different types of wing-bearing segments, illustrating diversity in
development of direct and indirect flight musecles. After Boudreaux Arthropod Phylogeny with
Special Reference to Insects Wiley 1979.
15 Generalized insect wings, with wing region and vein nomenclature. After Wootton Systematic
Entomology 4: 81-93, 1979.
16A-B Ovipositors of an ensiferan grasshopper (Tettigonia): A lateral view; B transverse section.
'Dorsal valve ' is the distal part of ‘3.valvula’ = coxopodite onIX. 'Inner valve' is the gonapophysis
on IX (=’2.valvula’). 'Anterior valve' is the gonapophysis of VIII (=’1.valvula’). After Davies,
Outlines of Entomology, Chapman & Hall 1988.
C Timema (basal phasmatodean). After Tilgner Mitt. Mus. Nat.kd. Berl., Dtsch entomol. Z 46: 149162,
D-F Mantophasma zephyra facies (D), female genital segments, lateral (E), male genital segments
lateral (F) C: coxite; cc: cercus; ep: dorsum XI (‘epiproct’); gp, gonapophysis; pp, (paired) venter
XI (‘paraprocts’); S: sternum; sp: sternal process; T: tergum. Klaus-D. Klass del.
17A Hypopharynx of a 'psocopteran'. Redrawn after Badonnel, here from Kristensen Systematisk
Entomologi, Munksgaard 1970.
B Head capsule of ’elephant louse’, Haematomyzus (Psocodea-Phthiraptera); note the unusual
mandibles and the equally unusual relative size of their ad-and abductors. After Weber Zoologica
41, 1969
C Mouth stylets of a sucking louse, Haematopinus. Redrawn after Ramcke, here from Kristensen
Systematisk Entomologi, Munksgaard 1970.
D Mechanism of stylet protrusion in a hemipteran, diagram; notice contractions of stylet protruder
muscles, and the function of the muscular ‘clamp’ in the labium.
E Telo- (or acro-)trophic ovariole type as occurring in, i.a., the Hemiptera.
F Alimentary canal of cicadomorph hemipteran, with ‘filter chamber’.
D-F Redrawn after Weber (D-E) and Goodchild (F), here from Kristensen Systematisk Entomologi,
Munksgaard 1970.
18 Summary cladogram of the principal endopterygote lineages. Thin single and double lines
indicate, respectively, monophyla and paraphyletic assemblages with <1000 described species; bold
and shaded lines indicate, respectively, monophyla and paraphyletic assemblages with 1 000 - 10
000 species. For clades with >10 000 described species the approximate species number is indicated
by the width of the clade line; scale in lower right corner.
ADE: Adephaga; ANN: Annulipalpia; ARC: Archostemata; APO: Apocrita; asi: asiloid
assemblage; BIB: Bibionomorpha; BIT: Bittacidae; BOR: Boreidae; bos: bostrichiform assemblage;
CEP: Cephoidea; CLE: Cleroidea; CUL: Culicomorpha; CUC: Cucujoidea; CYC: Cyclorrhapha;
DIT: Ditrysia; ELA: Elateriformia; EMP: Empidoidea; EXO: Exoporia; INT: Integripalpia; LYM:
Lymexylonoidea; MED: Megalodontoidea; MEG: Megaloptera; MER: Meropeidae; moh:
monotrysian Heteroneura; MYX: Myxophaga; NAN: Nannochoristidae; nco: non-culicomorph
oligoneuran non-neodipterans; nem: nemestrinoid assemblage; NEU: Neuroptera; ngl: nonglossatan assemblage; nml: non-neolepidopteran Glossata; ntp: non-tipuloid polyneuran
nematocerans; ORU: Orussoidea; PAN: Panorpomorpha; PHY: 'Phytophaga'
(=chrysomeloid/curculionoid assemblage); RAP: Raphidoptera; SIP: Siphonaptera; sir: siricoid
assemblage; spi: spicipalpian assemblage; STA: Staphyliniformia; STR: Strepsiptera; TEB:
45
Tenebrionoidea; TEN: Tenthredinioidea; TIP: Tipuloidea; txs:
tabanomorph/xylophagomorph/stratiomyomorph assemblage; XYE: Xyeloidea. After Kristensen,
Eur. J. Entomol.96: 237-253, 1999.