Cuticular ultrastructure in some marine oligochaetes (Tubificidae)

The ultrastructure of the thin, non-cellular cuticle is described for 6 mar ine oligochaetes, representing 3 of the subfamilies (Phallodrilinae, Limnod riloidinae, and Rhyacodrilinae) of the Tubificidae. The main components of the cuticle in these 6 species, as in most other oligochaetes examined, are : (1) a fiber zone closest to the epidermis, consisting of collagen fibers embedded in a matrix, (2) an epicuticle, which is a continuation of the mat rix outside the fiber zone, and (3) epicuticular projections, which are mem brane-bound bodies covering the outer surface of the epicuticle. The projec tions are probably formed by the microvilli that penetrate the cuticle from the epidermal cells below, but this was confirmed only in the studied limn odriloidines. Three of the species examined, Duridrilus tardus, Olavius vac uus, and Heterodrilus paucifascis, lack microvilli. The morphology of the c omponents in the cuticle differs between the studied species. The collagen fibers may form an "orthogonal grid" (i.e., layers of parallel fibers perpe ndicular to the layers immediately above and below), or they may form paral lel layers, or be irregularly scattered. The number of dense layers in the epicuticle, as well as the shape and internal structure of the epicuticular projections, also vary. All these characters might be useful in future phy logenetic analyses to achieve better hypotheses of relationships within oli gochaetes as well as to other groups.