EUSPERMATOZOA, PARASPERMATOZOA AND SPERMATOZEUGMATA OF LITTORARIA (PALUSTORINA) ARTICULATA (PROSOBRANCHIA, CAENOGASTROPODA) WITH SPECIAL REFERENCE TO THE PSEUDOTRICH

Paraspermatozoa and euspermatozoa of the littorinid gastropod Littorar ia (Palustorina) articulata are examined using transmission electron m icroscopy and light microscopy. In the seminal vesicle, both sperm typ es occur, either as free cells or organized into spermatozeugmata. It is shown that the elongate (120-140 mum), flagellum-like component of the paraspermatozoon is in fact a tubular extension of the plasma memb rane which encloses granular material but no axonemes or microtubules. This structure, here termed the pseudotrich, shows no evidence of mot ility and its function remains obscure. The main body region of the pa raspermatozoon (length 32-36 mum) contains numerous spherical vesicles , scattered mitochondria, one or two large, rod-shaped bodies (length 20-24 mum) and a fusiform, granular body (containing DNA; probably a m odified nucleus). The rod-shaped bodies, granular body and surrounding matrix are contained by a common membrane, and are therefore separate d from other contents of the paraspermatozoon. In each spermatozeugma, euspermatozoa are attached via the tips of their acrosomes to the par aspermatozoan body at the opposite end to the pseudotrich. Euspermatoz oa exhibit a conical acrosomal complex (with axial rod and basal plate ), a tubular nucleus sheathing the axoneme, a midpiece (5-6 helical mi tochondrial elements sheathing the axoneme), an annulus (with two ring s), a glycogen piece and an end piece (total sperm length 268-272 mum) . The euspermatozoa of L. articulata are similar to those of most litt orinids and many other caenogastropods. The presence of a pseudotrich in the paraspermatozoon appears to be restricted to the subgenus Palus torina.