Secondary microstructures in trilobite cuticles'
JOHN E . DALINGWATER
Dalingwater, J . E . 1 9 7 5 0 7 1 5 : Secondary microstructures in trilobite
cuticles. Fossils and S trata. No. 4. pp. 1 5 1 - 1 54. Pl. 1 . Oslo. ISSN 0 3 0 0 949 1 . I S B N 82-00-049 6 3 - 9 .
Descriptions are given of a variety of secondary microstructures in
trilobite cuticles, possibly due to the action of boring organisms, which
were encountered whilst studying primary microstruc ture . The majority
of these borings are considered to result from fungal activity .
f.E. Dalingwa ter, Departm ent of Zoology, The University, Manchester
M13 9PL, England, 1 5 th A ugust, 1 9 73
During a study of primary microstructure of the trilobite cuticle (Dalingwater 1 9 7 3 ) , various
secondary structures were encountered. Only those structures which can p ossibly be referred
to the action of epizoic, saprophytic or parastic organisms are considered here, as it is useful to
be able to distinguish these from primary microstructures. S tørmer ( 1 9 3 1 ) , in a paper discussing
boring organisms in trilo bite 'shells', reviewed the early literature, while Rolfe ( 1 9 6 2) summar­
ised subsequent work on borings in fossil arthropod cuticles. Other important and relevant
contributions are Hessland's ( 1 949) study of the action of 'penetrative and enveloping algae',
S tørmer's ( 1 96 3 ) detailed account of the micro-organisms associated with the cuticle of a
fossil scorpion, B romley's ( 1 9 7 0) extensive general review of borings as trace fossils, and
Taylor's ( 1 9 7 1 ) description of thallophyte borings in decapod and brachiopo d shells from the
Lower Cretaceous of Alexander Island.
This topic seems complex, as do most considerations of traces of animal or plant activities,
rather than of the organisms themselves, but a few general considerations can brie fly be outlined :
( 1 ) B orings in cuticles may be the result of:
( a) p enetration during the life of the 'host' commencing from either the inner or outer margin
of the cuticle.
( b) penetration immediately after ecdysis or the death of the animal, which may also commence
from either the inner or out er margin.
(c) penetration some time after ecdysis or the death of the 'host', in which case it may proceed
preferentially from one margin, because of chemical or physical differences be tween inn er and
outer margins ( or, for example, if the cuticle was p artIy buried in sediment) .
( 2) Different species, even organisms belonging to different phyla, may produce similar borings
under similar conditions. Alternatively, the same species may p roduce different types of
borings i n different conditions ( at different stages in i t s life cycle, in different types of shell, o r
in different regions of the same shell) . It is therefore difficult to apply Linnaean nomenclature
to borings.
( 3) Organisms recorded as responsible for borings in fossil shells are algae, fungi, bryozoans,
cirripedes, sponges, and worms. Of these, only fungi have been recorded as decomposing
chitin (Richards 1 95 1 ) . O ther chitinoclastic groups are bacteria (Campbell and Williams 1 95 1 )
and actinomycetes (Waksman 1 95 9) , most decomposition o f chitin i n nature being attributed
to the former group.
Only larger borings which penetrate the cuticle are described here. The cuticle/matrix
boundary in many slices is indistinct, possibly the result of activity of endolithic algae - this
aspect will be discussed in a later pap er. It is p ossible that the outermost layer isolated on
decalcification of the cuticle of A sap hus raniceps D alman with E.D.T.A. (Dalingwater 1 9 7 3)
is not primary but the result of endolithic algal activity.
I am mos t grateful to Dr. B . Taylor, Dr. G. Taylor and Dr. J. Miller for help and advice during the course of
the work, and to Mr. B . Atherton for photographic services. Part of the study was carried out during the
tenure of an S . R.C. S tudentship.
15 1
MATERIAL AND METRODS
Thin-sections prepared for a study of primary microstructure were re-examined for traces of
the activity of boring organisms. The maj ority of these thin-sections are of the lower 'Raniceps '
limestone, Raget, O land, S weden, and most of the borings are in trilobite cuticles from that
locality. In the descriptions that follow the material is from the lower 'Raniceps ' limestone
unless otherwise indicated. Details of borings can best be seen in fairly thick slices ( 3 0 Jl or
more thick) bu t these are difficult to photograph satisfactorily, so some slices were re-ground.
Preliminary studies of etched blocks and etched slices with the S canning Electron Microscope
have not yet yielded useful results. All preparations are stored in the Department of Zoology,
University of Manchester, England.
DESCRIPTIONS OF TRE BORINGS
SLICE O l. 0. 8 . 1 . Includes a tangential perp endicular section (Tan.P.S . ) of a pygidium,
possibly of an illaenid. The inner margin of the cuticle is almost completcly filled with a dark
mass of pyrite impregnated tubes which penetrate in to and occasionally almost through the
cuticle, including fine tubes 1 - 3 Jl in diameter filled with pyrite, wider tubes 6-8 Jl in diameter
less heavily impregnated with pyrite, and larger club-shaped structure s (Pl. 1 : 1 ) . B ranching of
tubes is rare. A similar range of structures is se en on the inner m argin of a transverse perp endi­
cular section (T.P.S . ) of a thoracic segment possibly belonging to A saphus raniceps D alman
(Stice Ot. A . l l b. 2, Pl. 1 :2 ) .
-
SLICE O l. 0 . 3 6 . 2 . - Longitudinal perpendicular section (L.P . S . ) o f the thoracic axis of
A. raniceps. Fine tubes ( 1 - 2 Jl in diameter) are concentrated on the outer edge of the cuticle,
while wider tubes ( 8- 1 0 Jl in diameter) , which sometimes branch dichotomously, penetrate
in to the cuti C Ie (Pl. 1 :3 ) . Both types of tube are accentuated by pyrite impregnation. A
somewhat similar series of tubes penetrate the cu ticle of an unidentified species (S tice Ol.
0. 1 1 0. 1).
SLICE O l. 0.45 . 3 . - Tan. P.S. across the edge of the cephalon of A mp y x nasu tus Dalman.
Twisted ribbon-like structures 2-4 Jl wide extend along the cuticle near its outer edge, but
sometimes extend deep into the cuticle (Pl. 1 :4) . I t is difficult to perceive any detail in the
ribbons, which have a distinct orange colouration. They seem to be related to the endolithic
algal borings at the cuticle/matrix boundary. S imilar orange ribbon-like sturctures are just
visible in the outer region of the cuticle in an L.P.S. of a pygidium, probably of A . raniceps
(Stice Ol. 0. 6. 1).
S LICE O l. 0. 1 0 2. 1 . - Tan.P.S . of a fragment of cuticle, possibly belonging to A . ran iceps.
The cuticle contains masses of pyrite impregnated thread-like structures, some forming
circular masses, others elongate skeins (Pl. 1 :5 ) . Individual threads, where distinguishable, are
about 1 Jl wide, and the maj ority are irregularly thickened by small no dose SWellings. S omewhat
similar structures are present in the outer area of the cephalic doublure in an L.P.S. of A. rani­
ceps (Stice Ol.A. 1 8. 2 ) .
SLICE O l. A . 2 7 . 1 . - L.P.S. through the pleural region o f a thorax, probably o f A . raniceps.
S traight, unbranched, pyrite impregnated tubes 2-4 Jl in diameter penetrate the cuticle and its
surrounding matrix, particularly shell fragments (Pl. 1 :6) . Apparent concentration of tubes
within shell particles may be because they are readily visibly in these areas, their pyrite
impregnation affording good contrast with calcite.
SLICE Ol. B.e . 1 b. 2 . - Tan.P.S. of the pygidium of Bo edaspis enszfer Whittington and B ohlin,
Expansus Limestone , Raget, O land. In all sections of this cuticle, fine tubes 2-4 Jl in dia­
meter extend along the inner margin of the cuticle and p ass across the cuticle at various angles.
The appearance of these tubes is fragmentary, possibly due to patchy impregnation with
pyrite (Pl. 1 : 7) .
SLICE Dy. E . 7 . 1 . L.P.S. through the posterior edge of the cranidium of Encrinurus
punctatus Wahlenberg, Wenlockian, Dudley, Worcs. , England. B oth edges of the cuticle are
heavily impregnated with pyrite, but the central area is clear. In this area primary fine and
wider perpendicular canals are accentuated by pyrite and show Rolfe's ( 1 96 2) 'Christmas-
152
tree effect', p ossibly due to growth of pyrite al ong laminae. In the posterior part of the
section tubes, 1-4 /1 in diameter, similar in appearance to the fine perpendicular canals, are
disposed at various angles to the perpendicular (Pl. 1 :8 ) ; these are considered secondary.
S ome tubes branch, although much app arent branching may be due to individual tubes
crossmg.
DISCUSSION
Most of the structures described above can probably be attributed to the action of some type
of boring organism. Their occurrence is 'casual' S tørmer ( 1 9 3 1 ) and for this reason it is difficult
to make a planned study in isolation from, for example, a study of primary microstructure.
Most boring systems occur in only one cuticle in a block, indicating that incorp oration of
the cuticle within the sediment probably to ok place after transp ort from a localised environ­
ment where the action of boring organisms was prevalent. Only one example (Slice Ol. A . 2 7. 1)
is described in which post-lithification penetration of a cuticle has certainly occurred.
Insufficient examples are described to make firm conclusions as to preference of establish­
ment on the inner or outer edges of the cuticle. There would seem to be physical differences
between the edges and centre of cuticles and, if the trilobite cuticle resembled that of other
arthropods, physical and chemical differences between inner and outer edges of exuviae or
complete cuticles.
Again, insufficient material is described to make possible a detailed classification of
different types. Each boring system described has unique features, and to complicate matters
further, might well be the result of the activities of a number of different types of organism.
However, certain similarities between types have already been noted in the descrip tions and
the following groupings are suggested :
( l ) S tructures forming a mat on both edges of the cuticle and penetrating inwards from both
sides (Slice Dy. E. 7. 1 ) .
( 2 ) S tructure forming a mass on one edge o f the cuticle with various structures penetrating
inwards (Slices Ol. 0. 8. 1 and Ol. A. 1 1 b . 2).
(3) More or less straight tubes, which rarely branch, penetrating the cuticle (Slices Ol. O. 3 6. 2
and Ol. o. 1 1 0. 1 ) , o r both cuticle and matrix (Slice Ol. A . 2 7. 1 ) .
(4) Irregular ribbon-like material forming skeins which generally extend along the cuticle
(Slices Ol. O. 45. 3 and Ol. O. 6. 1 ) .
( 5 ) Irregular thread-like masses, forming aggregations towards the centre of the cuticle (Slices
Ol. A. 1 02. 1 and Ol. O. 1 8. 2 ) .
I t is extremely difficult t o as sign responsibility for the borings t o particular groups. N one
resemble the borings described by S tørmer ( 1 9 3 1 ) from trilobite cuticles, but those described
from Slice Dy. E. 7. 1 show a strong resemblance to those figured by Hessland ( 1 949) . For the
reasons outl ined by Taylor ( 1 9 7 1 ) discussion of responsibility for the described borings can
be limited to the Algae, Fungi and Actinomycetes. Dr. G. Taylor (Botany Department,
Manchester University, pers. comm.) considered that the borings are too large to be referable
to the Actinomycetes. Bromley ( 1 96 5 ) outlined various criteria to distinguish algal and fungal
borings, indicating that no one of his criteria can be regarded as diagnostic, yet a group of
features taken together can add weight to an interp retation. Fungal borings are generally finer
than those of algae ( 1- 2 /1 as opposed to 6- 1 5 /1 ) ; their diameter is more or less constant; false
ramification is characteristic of algae; angle of branching is more constant in fungi; and finally,
the articles in �ungi tend to be more or less straight or gently curved, whilst those of algae are
sometimes very irregular. On these criteria borings in Slices Ol. O. 8. 1, Ol. A . 1 1 b. 2, Ol. O.
36.2, Ol. O. 1 1 0. 1 , Ol. O. 2 7. 1 , and Ol. B . e. 1 b . 2 can possibly be referred to the action of
fungi. In contrast, borings in Slices Ol. O . 45. 3, Ol. O . 6. 1 and Ol. O . 1 02. 1 are referred to the
algae. In particular, there seems a strong resemblance between the borings in the latter slice
and those of the green endolithic alga Gomontia p olyrhiza from a Recent oyster shell, figured
by Bathurst ( 1 9 7 1 ) .
153
RE FERENCES
Bathurst, R.G.C. 1 9 7 1 : Carb onate Sediments and their Diagenesis. 6 2 0 pp. Elsevier, Amsterdam, London,
New York.
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Co mparable Horiz ons. 355 pp. Ph .D. Thesis, University of London .
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and J . C . Harper (eds . ) Trace Fossils, 49-9 0 . Seel House Press, Liverpool.
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Ordovician penetrative and enveloping algae from the Siljan district. Bull. Geo!. Instn. Univ. Upsala 33,
409-42 8 . Uppsala.
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Størmer, L. 1 9 6 3 : Gigan toscorpio willsi, a new scorpion from the Lower Carboniferous of Scotland,
and its
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associated preying micro-organisms. Skr. norske Vidensk . -A kad. 8, 1 - 1 7 1 , Oslo .
Taylor, B.J . 1 9 7 1 : Thallophyte borings in phosphatic fossils from the Lower Cretac eous of south-east
Alexander Island, Antarctica. Palaeontology 1 4, 294-3 0 2 . London.
Waksman, S . A. 1 9 59 : The A c tinomycetes: I. Nature, Occurrence and A c tivities. 3 2 7 pp., Williams & Wilkins,
Baltimore.
Pla te 1
F ig. 1 . S lice O l. O 8 . 1 . X 1 2 5 . F ig. 2 . S lice O l. A . l l b . 2 . X 1 5 0. F ig. 3 . S lice O l. 0. 3 6 . 2 . X 1 20.
F ig. 4. S lice O l. 0 . 45 . 3 . X 1 00. F ig. 5 . S lice O l. 0 . 1 0 2 . 1 . X 1 8 0 . F ig. 6 . Slice O l. A . 2 7 . 1 . X40.
F ig. 7 S lice O l. B .e. 1 b . 2 . X 1 7 0 . F ig. 8. Slice Dy. E. 7 . 1 . X 1 2 5 .
154