AN ULTRASTRUCTURAL-STUDY OF SPERMATOZOA OF THE MAJIDAE WITH PARTICULAR REFERENCE TO THE ABERRANT SPERMATOZOON OF MACROPODIA-LONGIROSTRIS (CRUSTACEA, DECAPODA, BRACHYURA)

A total of 17 species, in 14 genera of majids have been examined for s perm ultrastructure. The present account describes the sperm of six of these species, in two subfamilies: Pisinae-Sphenocarcinus orbiculatus and Sphenocarcinus stuckine and Inachinae-Cyrtomaia furici, Grypacheu s hyalinus, Platymaia rebierei and Macropodia longirostris. M. longiro stris has the only eubrachyuran sperm in which the acrosome is known t o depart radically from a subspheroidal form. The acrosome is semiluna r in shape and is bordered by a very thin layer of cytoplasm and an un usually uniform, narrow band of chromatin. The apical surface of the a crosome is almost flat, though slightly concave, whereas the posterior surface forms a hemisphere, and is almost completely occupied by the thin, centrally perforate, electron dense operculum. The bulk of the a crosome consists of a homogeneous, moderately electron dense outer acr osome zone. This surrounds a small inner acrosome zone internal to whi ch is an ellipsoidal, pale perforatorium capped by a central acrosome zone. Majid sperm are distinguished by a flattened and/or centrally de pressed operculum; a further characteristic is that the pointed perfor atorium is relatively short and frequently does not reach the operculu m. They vary inter alin with regard to presence or absence of a poster ior median process and, apparently, of centrioles and of microtubules in the nuclear arms, and in the number of these arms. Perforation of t he operculum, seen in the Pisinae, is not constant in the Inachinae. S permatozoal ultrastructure offers no certain support for a close relat ionship of majids with parthenopids or hymenosomatids. (C) 1998 The Ro yal Swedish Academy of Sciences. Published by Elsevier Science Ltd. Al l rights reserved.