Current Microscopy Contributions to Advances in Science and Technology (A. Méndez-Vilas, Ed.)
Microscopic anatomy of aquatic oligochaetes (Annelida, Clitellata): a
zoological perspective
Carlos Caramelo and Enrique Martínez-Ansemil
Departamento de Bioloxía Animal, Bioloxía Vexetal e Ecoloxía, Facultade de Ciencias, Universidade da Coruña, Campus
da Zapateira s/n, 15071 A Coruña, Spain
The taxonomic identification of oligochaetes (clitellate annelids) mainly relies on internal organs due to the simplicity of
their external anatomy. This fact, added to the small size of most of the aquatic oligochaetes (“microdriles”) has made the
microscope an indispensable tool of study. In this paper we summarize the contribution of different microscopical
techniques - optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and
confocal laser scanning microscopy (CLSM)- to the growing knowledge on aquatic oligochaetes from a zoological
perspective. The use of the optical microscope has been essential for taxonomical studies, ever since the first descriptions
of aquatic oligochaetes made by Müller (1773) to the currently known ca.1700 species. During the last four decades,
electron microscopy has generated new scenarios. Thus, TEM contributed to subcellular and physiological studies, mainly
on sense organs, muscles and spermatozoa. In this context, it is worth noting that the ultrastructure of spermatozoa
provided interesting topics for discussion on the phylogeny of the Clitellata. Studies with SEM, mainly focusing on
chaetae, sense organs and mating structures, provided interesting insights on the field of the functional anatomy of worms.
The number of papers published based on observations with CLSM on aquatic oligochaetes is reduced and these are
mostly devoted to the structure of nervous system and its regeneration after fragmentation, together with embryonic
development of the musculature.
Keywords Annelida; aquatic oligochaetes; optical microscopy; TEM; SEM; CLSM
1. Introduction
Oligochaetes are hermaphroditic clitellate annelids, without suckers and provided with chaetae and spacious coelom.
External anatomy of these segmented worms is apparently simple. Hence, the clitellum -a thickened glandular region in
the body wall which produces the cocoon-, and the chaetae -usually four bundles protruding from the body wall of each
mesosomial segment-, generally represent the only two distinctive elements of their external anatomy. As a
consequence, the identification of oligochaetes mainly relies on internal organs such as: genitalia, digestive tract,
pharyngeal glands, nephridia and a few other structures (Fig. 1).
Oligochaetes are widely distributed and diversified in terrestrial and aquatic habitats, including the marine
environment. About one-third of the almost 5000 currently known species of oligochaetes are aquatic. Aquatic
oligochaetes are generally small-sized annelids (“microdriles”), ranging from 1 mm to a few centimeters in length and
50 to 500 µm in diameter. In fact, most of the about 1700 aquatic species known to date belong to one of the 13
microdrile families, which are truly aquatic with the only exception of the primarily terrestrial family Enchytraeidae.
Only about 60 species of “megadriles” have been found in aquatic habitats [1].
The aim of this paper is to summarize the growing knowledge on aquatic oligochaetes from a zoological perspective,
using different microscopic techniques: optical microscopy, transmission electron microscopy (TEM), scanning electron
microscopy (SEM) and confocal laser scanning microscopy (CLSM).
2. Historical background
The small size of aquatic oligochaetes has made the microscope an indispensable tool ever since the first observations
and descriptions of species were produced. The diagnosis of the first species described were superficial and essentially
based upon the external anatomy of some naidines (Stylaria lacustris (Linnnaeus, 1767), Nais elinguis Müller, 1773;
Dero digitata (Müller, 1773), Dero (Aulophorus) furcatus (Müller, 1773), Ophidonais serpentina (Müller, 1774), Nais
barbata Müller, 1774), tubificines (Tubifex tubifex (Müller, 1774)), lumbriculids (Lumbriculus variegatus (Müller,
1774)) and enchytraeids (Lumbricillus lineatus (Müller, 1774)).
The pace at which new species of aquatic oligochaetes were described using the optical microscope was slow over a
century. Thus, in the early seventies of the 19th century, hardly fifty species belonging to twenty genera were known.
Thereafter, the description of new species of aquatic oligochaetes increased exponentially to reach the ca. 1700
currently known [1]. In the last third of the 19th century, the great development of the knowledge of the diversity of
aquatic oligochaetes was accompanied with some anatomical studies of extraordinary accuracy (e.g. [2]). (Fig. 2).
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Current Microscopy Contributions to Advances in Science and Technology (A. Méndez-Vilas, Ed.)
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dsc
pr
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p
a
spt
pe
ov
vd
t
mf
pn
o
ff
vsc
spp
sc
fp
mp
pc
Fig. 1 Schematic drawing of the anterior region of a tubificine (Naididae) showing the genital region: (a) atrium; (c) clitellum; (dsc)
dorsal somatic chaetae; (ff) female funnel; (fp) female pore; (mf) male funnel; (mp) male pore; (o) ovary; (ov) ovisac; (p)
prostomium; (pc) penial chaetae; (pe) peristomium; (pr) prostate; (sc) spermathecal chaeta; (spp) spermathecal pore; (spt)
spermatheca; (sv) seminal vesicle; (t) testis; (vd) vas deferens; (vsc) ventral somatic chaetae.
At the beginning of the 20th century, Michaelsen [3] established a complete and elaborate classification that can be
regarded as the stem of all subsequent ones. This classification, intended to discriminate among families, selected a set
of characters that would remain on use in the future [4-7]. The location and number of different components of the
genital apparatus, with special attention to the number of testes and ovaries, and the relative position of spermathecae,
genital pores and sperm funnels were the main characters in which these classifications were based. Details of almost all
of the anatomical structures observable with optical microscopy were used for species diagnosis: somatic chaetae,
presence, number and type of prostates, development of atria and vasa deferentia, presence and shape of structures for
sperm transfer (genital chaetae, pseudopenes, penes, cuticular sheaths), shape of spermathecae, presence of
espermatozeugmata, presence and type of coelomocytes, shape of nephridia, etc. (Figs 3-12).
In the eighties and early 90's, the studies both on aquatic oligochaetes and other zoological taxa aimed to organize the
diversity of groups according to a natural classification system. Hence, a growing body of literature appeared from the
prespective of Cladistics (e.g. [8-10]). However, discrepancies among authors when considering the supposed
homology of many of the characters used as indicators of relationship arouse, and often derived in highly contradictory
conclusions [11]. As a consequence, phylogenetic studies based on anatomical characters declined in favor of
molecular-based phylogeny. Nevertheless, given the importance of the anatomical knowledge to generate interesting
hypothesis in the field of phylogeny, some authors keep on devoting to fine anatomy studies, even attempting to
elucidate the embryonic origin of some structures [12-14].
In spite of the microscope being in decline as a tool to study the diversity of aquatic oligochaetes, new genera and
even higher-level taxa are still being described nowadays [15-20].
The earliest studies performed with transmission electron microscopy (TEM) on aquatic oligochaetes date from the
50's and mainly focused on the description of embryonic subcellular structures (e.g. [21-24]). Jamieson ’s revision [25]
on the ultrastructure of the oligochaete showed that 20% of the more than 300 papers published to date using the TEM
were devoted to the study of aquatic oligochaetes. These studies were generally patchy and focused on a few structures:
epidermis, clitellum, sensory organs, coelomocytes, chloragogen cells, muscles, sperm (e.g. [26-32]). Most of these
studies have a clear physiological orientation whereas only some of them aim for a zoological perspective,
incorporating new elements of discussion in the field of systematics (e.g. [31, 33]).
In the recent decades, TEM observations have been particularly focused on the muscle wall and the ultrastructure of
sperm. Papers on muscles were merely descriptive [34-36], and only some of them established comparisons among
taxa, under a taxonomic or phylogenetic orientation [37-39]. Most studies of sperm ultrastructure have a clear
phylogenetic orientation, providing interesting topics for discussion within the Clitellata [40-47]. (Figs 13, 14).
The first studies of aquatic oligochaetes using scanning electron microscope (SEM) date from the early 70’s [48].
Papers carried out since then to the end of the century were very scarce and focused almost exclusively on external
sensory organs [49-51] and somatic chaetae [52-58]. The few observations on sense organs complemented the initial
knowledge derived from the use of TEM, and the observations of somatic chetae were generally intended to
complement the diagnosis of some taxa, although in some cases [52, 55, 56] were used as a tool for tracking changes in
environmental conditions. Yáñez et al. [59] and Caramelo and Martínez-Ansemil [60] published two extensive studies
on the typology and distribution patterns of ciliated sense receptors in the main families of microdriles. In addition to
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Current Microscopy Contributions to Advances in Science and Technology (A. Méndez-Vilas, Ed.)
A
B
Fig. 2 In the last third of the 19th century, the great development in the knowledge of the diversity of aquatic oligochaetes was
accompanied with anatomical studies of extraordinary accuracy: two images from Vejdovský, 1884 [2]. A. Anterior region of
Chaetogaster diaphanus (Gruithuisen) (Plate V, fig. 1). B. Nephridium of Psammoryctides barbatus. (Grube) (Plate. IX, fig. 1).
these studies and some publications that show images of somatic chaetae with SEM, in 2001, Cuadrado and MartínezAnsemil [61] published the first work on attachment and sperm transfer. Recently, Caramelo and Martínez-Ansemil
[62] provided new insights into sensory organs, chaetae, mating systems, as well as about some other structures not
previously observed such as coelomic pores and genital marks (Figs 15-18).
The use of confocal microscopy techniques (CLSM) and / or imnunohistochemistry for the study of microdriles
started in the late 90's with the observations of the central nervous system of some species (e.g. [63, 64]). Molnár et al.
[65, 66] addressed the study of peripheral nervous system of one species of tubificine. In addition, Bergter and Paululat
[67] studied the embryonic development of the musculature, and Yoshida-Noro et al. [68] and Müller [69] performed
observations on the developing nervous system during regeneration after a process of fragmentation on different
species. (Figs 14-19).
3. Conclusions
Optical microscopy is an indispensable tool to ascertain the biodiversity of aquatic oligochaetes, knowledge that is
experiencing an exponential growing. In spite of the increasing number of molecular-oriented studies, some new
anatomical structures and many new taxa are still being described with optical microscopy, thus providing important
contributions in the field of taxonomy and phylogeny of the clitellates. Many questions are still to be solved, especially
those regarded to functional anatomy (mating systems, sensory organs, etc). In this context, the use of electron and
confocal microscopy is contributing important results that are expected to be increased in the next future.
Acknowledgements The authors wish to thank Dr. M. Quintela for proofreading and A. Castro and C. Sueiro, SAI (Universidade da
Coruña) for technical assistance with SEM, TEM and CLSM.
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10 11
d
Figs 3-12 Optical microscopy is an indispensable tool to ascertain the diversity in aquatic oligochaetes (microdriles). Many
anatomical structures are used for their identification. Fig. 3. Cernosvitoviella atrata (Bretscher), anterior body region. Fig. 4. Henlea
perpusilla Friend, anterior segments. Fig. 5. Lumbricillus rivalis (Levinsen), central nervous system. Fig. 6. Stylodrilus glandulosus
Giani & Martínez-Ansemil, transversal section segment X. Fig. 7. Tubifex tubifex (Müller), male apparatus. Fig. 8. Limnodrilus
udekemianus Claparède, cuticular penis sheath. Fig. 9. Psammoryctides barbatus (Grube), dorsal chaetae. Fig. 10. Amphichaeta
sannio Kallstenius, anterior body region. Fig. 11. L. rivalis, chaetal bundle. Fig. 12. Stylodrilus heringianus Claparède, chaetal
bundles. (at) atrium; (b) brain; (c) coelomocytes; (cc) circumpharyngeal connectives; (co) coelom; (d) diatoms inside the gut; (g) gut;
(m) mouth; (pb) penial bulb; (pe) penis; (pg) prostate gland; (ph) pharynx; (phg) pharyngeal glands; (php) pharyngeal pad; (pr)
prostomium; (rmp) retractor muscles of the pharynx; (sv) seminal vesicle; (vd) vas deferens; (vnc) ventral nerve cord.
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Current Microscopy Contributions to Advances in Science and Technology (A. Méndez-Vilas, Ed.)
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Figs 13-19 Electron microscopy and CLSM contribute with new insights to the zoological knowledge of aquatic oligochaetes. Fig.
13. Phylogeny of some Oligochaeta, using spermatozoal ultrastructure (phylogram for the sperm of 11 species), from Jamieson et al.
1987 [45]. Fig. 14. Prostomial pit of Bothrioneurum vejdovskyanum Stolc (TEM). Fig. 15. Genital chaeta of Potamothrix
hammoniensis (Michaelsen) (SEM). Fig. 16. Coelomic pore of Protuberodrilus tourenqui Giani & Martínez-Ansemil (SEM). Fig.
17. Ciliate sense receptor of Eiseniella tetraedra (Savigny) (SEM). Fig. 18. Genital region of Peristodrilus montanus (Hrabé)
(ventral view). Fig 19. Ventral nerve cord and nephridium of B. vejdovskyanum. (ab) anchorage bridge; (ci) cilium; (cu) cuticle; (ep)
epicuticular projections; (m) muscle; (mv) microvilli; (n) nephridium; (pc) penial chaetae; (vnc) ventral nerve cord; (za) zonula
adhaerens.
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References
[1] Martin P, Martínez-Ansemil E, Pinder A, Timm T, Wetzel MJ. Global diversity of oligochaetous annelids (“Oligochaeta”;
Clitellata) in freshwater. Hydrobiologia. 2008;595:117-127.
[2] Vejdovský F. System und morphologie der Oligochaeten. Praga: Franz-Rvinác; 1884.
[3] Michaelsen W. Oligochaeta. Berlin: Friedlönder & Sohn; 1900.
[4] Stephenson J. The Oligochaeta. Oxford: Clarendon Press; 1930.
[5] Yamaguchi H. Studies on aquatic oligochaeta of Japan. VI. A systematic report, with some remarks on the classification and
phylogeny of the Oligochaeta. J. Fac. Sci. Hokkaido Univ. Ser. VI, Zool. 1953;11:277-343.
[6] Chekanoskaya OV. Vadnye Maloshchetinkovye Chervy Fauny SSSR [Aquatic Oligochaeta of the USSR]. Leningrad:Akademia
Nauk SSSR. Zoologicheskii Institut. Akademia Nauk SSSR. 1962. Translated from Russian, New Dehli: Amerind Publishing Co.;
1981.
[7] Brinkhurst RO, Jamieson BGM. Aquatic Oligochaeta of the World. Edinburgh: Oliver & Boyd; 1971.
[8] Erséus C. Phylogenetic analysis of the aquatic Oligochaeta under the principle of parsimony. Hydrobiologia. 1987;155:75-89.
[9]. Erséus C. A generic revision of the Phallodrilinae (Oligochaeta, Tubificidae). Zool. Scr. 1992;21:5-48.
[10] Brinkhurst RO. Evolutionary relationships within the Clitellata: an update. Megadrilogica. 1994;5:109-112.
[11] Martínez-Ansemil E. Études sur les oligochètes aquatiques des pays du pourtour de la Méditerranée: taxonomie, phylogénie,
biogéographie et écologie. Thèse d’État. Université Paul Sabatier, Toulouse; 1993.
[12] Gustavsson LM, Erséus C. Morphogenesis of the genital ducts and spermathecae in Clitellio arenarius, Heterochaeta costata,
Tubificoides benedii (Tubificidae) and Stylaria lacustris (Naididae) (Annelida, Oligochaeta). Acta Zoologica (Stockholm).
1997;78:9-31.
[13] Gustavsson LM, Erséus C. Development of the genital ducts and spermathecae in the Rhyacodrilines Rhyacodrilus coccineus and
Monopylephorus rubroniveus (Oligochaeta, Tubificidae). J. Morphol. 1999;242:141-156.
[14] Gustavsson LM, Erséus C. Morphology and phylogenetic implications of oesophageal modifications in the Limnodriloidinae
(Oligochaeta, Tubificidae). J. Zool., Lond. 1999;248:467-482.
[15] Erséus C. Parvidrilus strayeri, a new genus and species, an enigmatic interstitial clitellate from underground waters in Alabama.
Proc. Biol. Soc. Wash. 1999;112:327-337.
[16] Pinder A, Brinkhurst RO. A review of the Tubuficidae (Annelida: Oligochaeta) from Australian inland waters. Memoirs of
Museum Victoria. 2000;58:39-75.
[17] Fend SV, Rodriguez P. Eremidrilus n. gen. (Annelida, Clitellata, Lumbriculidae) a new species from California, U.S.A. Can. J.
Zool. 2003;81:515-542.
[18] Wang H, Erséus C. New species of Doliodrilus and other Limnodriloidinae (Oligochaeta, Tubificidae) from Hainan and other
parts of the north-west Pacific Ocean. J. Nat. Hist. 2004;38:269-299.
[19] Fend SV, Lenat DR. Two new genera of Lumbriculidae (Annelida, Clitellata) from North Carolina, USA. Zootaxa. 2007;1666:122.
[20] Martin P, Martínez-Ansemil E, Sambugar B. The Baikalian genus Rhyacodriloides in Europe: phylogenetic assessment of
Rhyacodriloidinae subfam. nov. within the Naididae (Annelida). Zool. Scr. 2010;39:462-482.
[21] Lehman FE. Elektronenmikroskopische untersuchungen an den polplasmen von Tubifex und dem mikromeren von Paracentrotus.
Arch. Julius Klaus Stift. Vererbungsforsch. Sozialanthropol. Rassenhyg. 1950;25:611-619.
[22] Lehman FE. Plasmatische eiorganisation und entwicklungsleistung beim keim vom Tubifex (Spiralia). Naturwissenschaften.
1956;43:289-296.
[23] Lehman FE, Mancuso V. Verschiedenheiten in der submikroskopischen struktur des somatoblasten des embryos von Tubifex.
Arch. Julius Klaus Stift. Vererbungsforsch. Sozialanthropol. Rassenhyg. 1959;32:482-493.
[24] Weber R. Zur verteilung der mitochondrien in frühen entwicklungsstadien von Tubifex. Rev. Suisse Zool. 1956;63:277-288.
[25] Jamieson BGM. The ultrastructure of the Oligochaeta. London: Academic Press; 1981.
[26] Lanzavecchia G. Studi sulla muscolatura elicoidale e paramiosinica. Nota IV. La muscolatura longitudinale e circolare della parete
corporea degli Anellidi Tubificidi. Atti Accad. Naz. Lincei, Rend. Cl. Sci. Fis., Mat. Natur. 1971;50:50-56.
[27] Moritz K, Storch V. Elektronenmikroskopische untersuchung eines mechanorezeptors von evertebraten (Priapuliden,
Oligochaeten). Z. Zellforsch. 1971;117:226-234.
[28] Richards KS. The histochemistry and ultrastructure of the clitellum of the enchytraeid Lumbricillus rivalis (Oligochaete:
Annelida). J. Zool., Lond. 1977;183:161-176.
[29] Richards KS. The histochemistry and ultrastructure of the coelomocytes of species of Lumbricillus, and observations on certain
other echytraeid genera (Oligochaeta: Annelida). J. Zool., Lond. 1980;191:557-577.
[30] Sapaev EA. Fine structure of somatic and visceral muscles in Chaetogaster limmaei (Oligochaeta, Naididae). Zool. zh.
1977;56:17-22.
[31] Ferraguti M, Lanzavecchia G. Comparative electron microscopic studies of muscle and sperm cells in Branchiobdella pentodonta
Whitman and Bythonomus lemani Grube (Annelida, Clitellata). Zoomorphologie. 1977;88:19-36.
[32] Fischer E, Horváth I. Cytological and cytochemical studies on the chloragocytes of Tubifex tubifex Müll. with special regard to
their role in heme-metabolism. Zool. Anz. 1978;201:31-43.
[33] Golding DW, Whittle AC. Secretory end-feet, extracerebral cells, and cerebral sense organs on certain limicole oligochaete
annelids. Tissue Cell. 1975;7:469-484.
[34] Lanzavecchia G, de Eguileor M, Valvassori R, Lanzavecchia Jr P. Analysis and reconstruction of unusual obliquely striated fibres
in Lumbriculids (Annelida, Oligochaeta). Journal of Muscle Research and Cell Motility. 1987;8:209-219.
[35] Lanzavecchia G, de Eguileor M, Valvassori R, Di Lernia L, Cambiaso C. Morphogenesis of body wall muscle fibers in
Enchytraeus minutus. Hydrobiologia. 1989;180:91-97.
[36] de Eguileor M, Valvassori R, Lanzavecchia G, Di Lernia L. T-system in muscles of microdriles. Hydrobiologia. 1989;180:109114.
© 2012 FORMATEX
26
Current Microscopy Contributions to Advances in Science and Technology (A. Méndez-Vilas, Ed.)
[37] de Eguileor M, Lanzavecchia G, Valvassori R, Lanzavecchia Jr P. Unusual model of lumbriculids’ helical muscles: comparison
with body wall muscles in other microdriles. Hydrobiologia. 1987;155:135-144.
[38] de Eguileor M, Valvassori R, Lanzavecchia G, Giorgi S. Body wall muscles in the haplotaxids Haplotaxis gordioides and
Pelodrilus leruthi (Annelida, Oligochaeta). Zoomorphology. 1990;110:27-36.
[39] Valvassori R, de Eguileor M, Lanzavecchia G, Scari G. Body wall organization in enchytraeids. Hydrobiologia. 1989;180:83-89.
[40] Ferraguti M. The comparative ultrastructure of sperm flagella central sheath in Clitellata reveals a new autapomorphy of the
group. Zool. Scr. 1984;13:201-207.
[41] Ferraguti M, Jamieson BGM. Spermiogenesis in Bythonomus lemani and the phylogenetic position of the Lumbriculidae
(Oligochaeta, Annelida). Hydrobiologia. 1987;155:123-134.
[42] Erséus C, Ferraguti M. The use of spermatozoal ultrastructure in phylogenetic studies of Tubificidae (Oligochaeta). Mém. Mus.
natn. Hist. nat. 1995;166:189-201.
[43] Ferraguti M, Erséus C. Sperm types and their use for a phylogenetic analysis of aquatic clitellates. Hydrobiologia. 1999;402:225237.
[44] Ferraguti M, Erséus C, Kaygorodova I, Martin P. New sperm types in Naididae and Lumbriculidae (Annelida: Oligochaeta) and
their possible phylogenetic implications. Hydrobiologia. 1999;406:213-222.
[45] Jamieson BGM, Erséus C, Ferraguti M. Parsimony analysis of the phylogeny of some oligochaeta (Annelida) using spermatozoal
ultrastructure. Cladistics. 1987;3:145-155.
[46] Marotta R, Ferraguti M. Erséus C. A phylogenetic analysis of Tubificinae and Limnodriloidinae (Annelida, Clitellata, Tubificidae)
using sperm and somatic characters. Zool. Scr. 2003;32:255-278.
[47] Marotta R, Ferraguti M. Sperm ultrastructure in assessing phylogenetic relationships among Clitellate Annelids. In: Shain DH, ed.
Annelids in Modern Biology. Hoboken, NJ: Wiley-Blackwell; 2009:314-327.
[48] Van Hoven W. The penis sheats of Limnodrilus hoffmeisteri (Clap.) and Tubifex tubifex (Müller). A scanning electron microscope
study. In: Proceedings Southern African Electron Microscopy Society. Pretoria: CSIR Symposium S63; 1971:39-40.
[49] Chapman PM. The prostomial pit in Bothrioneuron vejdovskyanum Stolc (Oligochaeta): a note on detail revealed by SEM. Proc.
biol. Soc. Wash. 1979;92:812-813.
[50] Smith ME. External sense organs of Tubifex tubifex and Limnodrilus hoffmeisteri (Tubificidae). Freshwat. Invertebr. Biol.
1983;2:154-158.
[51] Römbke J, Schmidt M. REM documentation of putative cuticular sense organs of enchytraeids. Newsletter on Enchytraeidae.
1999;6:15-20.
[52] Milbrink G. Characteristic deformities in tubificid oligochaetes inhabiting polluted bays of Lake Vänern, Southern Sweden.
Hydrobiologia. 1983;106:169-184.
[53] Grimm R. Beiträge zur systematik der afrikanischen Naididae (Oligochaeta). II. Dero raviensis (Stephenson, 1914) und
Aulophorus africanus Michaelsen, 1914-zwei verbreitete afrikanische arten. Mitt. hamb. zool. Mus. Inst. 1985;82:109-117.
[54] Grimm R. Beiträge zur systematik der afrikanischen Naididae (Oligochaeta). III. Untersuchungen zur qualitativen und
quantitativen Chaetotoxonomie der Naididae. Mitt. hamb. zool. Mus. Inst. 1986;83:101-115.
[55] Chapman PM, Brinkhurst RO. Setal morphology of the oligochaetes Tubifex tubifex and Ilyodrilus frantzi (capillatus) as revealed
by SEM. Proc. Biol. Soc. Wash. 1986;99:323-327.
[56] Chapman PM, Brinkhurst RO. Hair today, gone tomorrow: induced chaetal changes in tubificid oligochaetes. Hydrobiologia.
1987; 155:45-55.
[57] Grimm R. Beiträge zur systematik der afrikanischen Naididae (Oligochaeta). VI. Naidinae (Teil 1). Mitt. hamb. zool. Mus. Inst.
1988;85:73-102.
[58] Grimm R. Beiträge zur systematik der afrikanischen Naididae (Oligochaeta) VII. Naidinae (Teil 2). Mitt. hamb. zool. Mus. Inst.
1989;86:107-126.
[59] Yáñez E, Cuadrado S, Martínez-Ansemil E. External sense organs in freshwater oligochaetes (Annelida: Clitellata) revealed by
Scanning Electron Microscopy. J. Morphol. 2006;267:198-207.
[60] Caramelo C, Martínez-Ansemil E. External sense receptors in microdrile oligochaetes (Annelida, Clitellata) as revealed by
Scanning Electron Microscopy: typology and patterns of distribution in the main taxonomic groups. J. Morphol. 2010;271:14821492.
[61] Cuadrado S, Martínez-Ansemil E. External structures used during attachement and sperm transfer in tubificids (Annelida,
Oligochaeta). Hydrobiologia. 2001;463:107-113.
[62] Caramelo C, Martínez-Ansemil E. Morphological investigations of microdrile oligochaetes (Annelida, Clitellata) using scanning
electron microscopy. Turk. J. Zool. 2012;36:1-14
[63] Hessling R, Westheide W. CLSM analysis of development and structure of the central nervous system of Enchytraeus crypticus
("Oligochaeta", Enchytraeidae). Zoomorphology. 1999;119:37-47.
[64] Hessling R, Müller MC, Westheide W. CLSM analysis of serotonin-immunoreactive neurons in the central nervous system of
Nais variabilis, Slavina appendiculata and Stylaria lacustris (Oligochaeta: Naididae). Hydrobiologia. 1999;406:223-233.
[65]. Molnár L, Kiszler G. Pollák E, Deres L. Distribution pattern of gamma-amino butyric acid and immunoreactive neural structures
in the central and peripheral nervous system of the tubificid worm, Limnodrilus hoffmeisteri. Hydrobiologia. 2006;564:33-43
[66] Molnár L, Kiszler G, Pollák E. Identification and pattern of primary sensory cells in the body wall epithelium of the tubificid
worm, Limnodrilus hoffmeisteri. Hydrobiologia. 2006;564:45-50.
[67] Bergter A, Paululat A. Pattern of body-wall muscle differentiation during embryonic development of Enchytraeus coronatus
(Annelida: Oligochaeta; Enchytraeidae). J. Morphol. 2007;268:537-549.
[68] Yoshida-Noro C, Myohara M, Kobari F, Tochinai S. Nervous system dynamics during fragmentation and regeneration in
Enchytraeus japonensis (Oligochaeta, Annelida). Dev. Genes Evol. 2000;210:311-319.
[69] Müller MCM. Nerve development, growth and differentiation during regeneration in Enchytraeus fragmentosus and Stylaria
lacustris (Oligochaeta). Develop. Growth Differ. 2004;46:471-4.
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