The spermatozoan ultrastructure of the gonochoristic eutardigrades Pseudobiotus megalonyx, Ramazzottius tribulosus and Ramazzottius oberhaeuseri (Hypsibiidae, Hypsibiinae) are described and illustrated. The two species of the same genus have very similar spermatozoa, whereas the two genera differ widely in male gamete organization. The testicular spermatozoon of Pseudobiotus has a thread-like configuration and is made up of a small comma-shaped acrosome, a helical nucleus and a tail with terminal tuft; no middle piece or neck and mitochondria were observed. The testicular spermatozoon of Ramazzottius shows an evident rod-shaped acrosome, a cork-screwshaped nucleus and a short tubular middle piece containing a mitochondrial sleeve; moreover, the tail splits terminally into a tuft. Functional considerations and phylogenetic comparisons are made on the basis of sperm morphology.
Spermatozoon morphology of three species of Hypsibiidae (Tardigrada, Eutardigrada)and phylogenetic evaluation / Rebecchi, Lorena; Bertolani, Roberto. - In: ZOOLOGISCHER ANZEIGER. - ISSN 0044-5231. - STAMPA. - 238:(1999), pp. 319-328.