An Ultrastructural Study of Gametogenesis of the Marine Bivalve Pinna Nobilis (Linnaeus 1758)ii. Spermatogenesis

The fine structure of the spermatogonium, spennato-cyte, spermatids and spermatozoon of a marine bivalve, Pinna nobilis, is described. The structure of the spermatozoon is similar to that described for other bivalves of the subclass Pteriomorpha: a head comprising a round nucleus capped by a conical acrosome and a mid-piece of 4–6 mitochondria. The spermatozoon conforms to the basic ‘primitive type’ renamed ect-aquasperm. It typifies that of an externally fertilizing animal. Abnormal spermatogenesis is also described. Residual spennatozoaafter spawning are present in the cytoplasm of auxiliary cells. These auxiliary cells seem to play a trophic role only during the first stage of spermatogenesis.