SPERMATOZOON ULTRASTRUCTURE IN 2 SPECIES OF AMPHIBOLUS (EUTARDIGRADA,EOHYPSIBIIDAE)

We examined the ultrastructure of the spermatozoa from two species of eutardigrades, gonochoristic Amphibolus volubilis and hermaphoroditic A. weglarkae, by scanning and transmission electron microscopy. The ga metes from the two species were morphologically quite similar, each co nsisting of a short head, neck and tail. The head included a conic, co rkscrew-shaped, bilayered acrosome and a cylindrical nucleus with cond ensed chromatin. The nucleus is surrounded by cytoplasm organized in o void elements with an electron-dense core. The neck is very simple, co ntaining a centriole and unmodified mitochondria. The flagellum contai ns a 9+2 axoneme and terminates in a tuft of between eight and 10 micr otubules. The spermatozoa of Amphibolus, like those of the other eutar digrades, are of the modified type, but nonetheless maintain some prim itive aspects of the gametes from heterotardigrades.