The ultrastructure of the cuticle of some British lumbricids (Annelida)



The ultrastructure of the cuticle of 11 species of British lumbricids is described. The number of unbanded collagenous fibre layers varies with the species and is roughly proportional to the size of the adult worm. Four zones are discernible in the cuticle matrix in all species except E. foetida where the outermost zone shows subdivision.

Microvilli, cytoplasmic extensions from the epithelial surface, occur. The “long” and “short” microvilli of other workers are shown to be different views of the same structure. The microvilli have an ovoid base with the two poles forming low shoulders on either side of the ascending microvillus. The bases are oriented at right-angles to the longitudinal axis of the worm and the microvilli are arranged in regular staggered rows along the same axis. Details of the spatial alignment of the microvilli are given and the possible role of these regularly arranged structures as factors in the orientation of the collagen fibre unit filaments is discussed, and it is speculated that they might also have some proprioceptive function.

Distally the microvilli terminate among the surface epicuticular projections and are shown to give rise to them. The epicuticular projections are peanut-shell shaped with a distinct substructure consisting of a 8 nm electron dense lining and two parallel dense discs, each 8 nm deep, above the “waist”.

The mucous cell pores are lined with electron pale microfibrillar material and at the base of the pore a circlet of 13–15 short microvilli, with prominent tonofilaments, arises from the cytoplasm of the mucous cell. Surrounding the pore microvilli are numerous, small, membrane bound mucous pore particles.