Paraspermatogenesis in Littoraria (Palustorina) articulata, with referenceto other Littorinidae (Littorinoidea, Caenogastropoda)

The ultrastructure of paraspermatogenesis is examined in the littorinid sub family Littorininae, with special emphasis on Littoraria (Palustorina) arti culata (PHILIPPI 1846). In particular the study focuses on the fate of the nucleus and origin of the rod bodies during parasperm development. Parasper m of the Littorininae are rounded or oblong cells, which undergo an abortiv e meiosis and eliminate part of the nucleus but often retain a nuclear remn ant. The cytoplasm is filled with numerous spherical vesicles in all Littor ininae, but in Littoraria land in certain species of Nodilittorina, Tectari us and Cenchritis) dense 'rod-bodies' also occur. Littoraria (Palustorina) are unique in possessing a flagellum-like structure termed the 'pseudotrich ', which lacks an axoneme but contains microtubules during its development. Paraspermatogonia differ from euspermatogonia in the structure of the nucl eus and in the extensive rough endoplasmic reticulum (RER) and swollen cyto plasm. Two types of secretions develop in Littoraria: (1) numerous, spheric al granules (composed of putative glycoprotein, also seen in other Littorin inae) and (2) rhomboid granules (composition uncertain but reacting positiv ely to RNA stains; these granules arising within RER cisternae close to the nucleus). As the rhomboid granules fuse to form the larger, rod-bodies (po lygonal in cross section), the RER membrane enclosing the rod-bodies become s confluent with the outer nuclear membrane, thereby forming a common compa rtment. Results of this study clearly show that the rod-bodies are secretio ns of the RER cisternae and not, as claimed in some light microscopic accou nts, the product of fusion of eusperm nuclei which have entered the paraspe rm cytoplasm (either by active eusperm penetration or by phagocytosis). Dev elopmental characteristics of littorinid parasperm show differences between species and may, in some cases, provide characters diagnostic of subgenera .