Comparative study of the cuticle in some aquatic oligochaetes (Annelida: Clitellata)

Abstract

An examination of the cuticle of six aquatic oligochaete species using transmission electron microscopy revealed a larger morphological variation than previously known. Three freshwater species, Aulodrilus pluriseta, Spirosperma ferox (both Tubificidae), and Pristina breviseta (Naididae), and three marine species, Clitellio arenarius, Heterochaeta costata (both Tubificidae), and Paranais litoralis (Naididae), were investigated. The arrangement of the collagen fibers in the cuticle differs among the studied species. Only S. ferox shows an "orthogonal grid," i.e., layers of parallel fibers perpendicular to each other, as earlier described for lumbricids and enchytraeids. Clitellio arenarius and H. costata have fibers arranged in layers, while A. pluriseta and P. litoralis have irregularly distributed fibers. Pristina breviseta lacks cuticular fibers. The matrix surrounding the collagen fibers (when present) continues outside the fiber layer, making up a thin epicuticle, which has a unique banding in each of the studied species. The external surface of the epicuticle is covered with epicuticular projections. Their number, shape, and attachment to the epicuticle vary among the studied species. Furthermore, a distinctive internal substructure of the projections was observed in H. costata, A. pluriseta, S. ferox, and P. breviseta. Microvilli, extensions from the epidermal cells, penetrate the cuticle and terminate at its outer surface. In three species microvilli were observed to pinch off the epicuticular projections. The size, number, and shape of the latter vary; no typical microvilli were observed in S. ferox.

An ultrastructural study of the cuticle in the marine annelid Heterodrilus (Tubificidae, Clitellata)

“…A layered epicuticle has been reported for lumbricids (Richards, 1974), for some Brazilian earthworms (Rodriguez Alves et al, 1984), and for several groups of tubificids (Gustavsson and Erséus, 2000;Gustavsson, 2001), and the substructure of the epicuticle has been unique for each studied species. However, in this study, specimens of Heterodrilus paucifascis from different localities deviate in the morphology of the epicuticle.…”

“…Lack of an orthogonal grid was also reported by Giere (1983) for two tubificids, Thalassodrilus prostatus and Aktedrilus monospermathecus, and by Jamieson (1992) in the naidine Chaetogaster limnaei. The findings by Gustavsson and Erséus (2000) and Gustavsson (2001) show that the Tubificidae encompass a larger variation in the morphology of the cuticle than previously known; these authors concluded that the variation could be associated with phylogenetic relationships. However, thus far the cuticle has only been described at the species level, and the amount of interspecific variation of the morphology of the cuticle is not known.…”

“…Hat-shaped or fungiform projections, with the widest part closest to the surface of the epicuticle are found in Slavina evelinae (Gluzman, 1992). In Pristina breviseta (Gustavsson, 2001), the projections are triangular with one of the sides towards the cuticular surface and with buds/vesicles bulging from them. The epicuticular projections in most specimens of Heterodrilus are club-shaped with the broader end pointing outwards.…”

“…They are basically ellipsoid but deviations from this shape occur. In Enchytraeus formosus (Hess and Menzel, 1967) and Aulodrilus pluriseta (Gustavsson, 2001), the projections are ellipsoid, with slender extensions from their distal part. Hat-shaped or fungiform projections, with the widest part closest to the surface of the epicuticle are found in Slavina evelinae (Gluzman, 1992).…”

“…In recent years, however, several morphological investigations on systems other than the reproductive have been performed on different groups of annelids. Sensory organs in sedentary polychaetes were studied by Purschke and Hausen (2007), the ultrastructure of phaosomous photoreceptors was studied in Stylaria lacustris (Purschke, 2003), and cuticular morphology in oligochaetes was studied by Gustavsson and Erséus (2000) and Gustavsson (2001).…”