SPERMIOGENESIS AND SPERM ULTRASTRUCTURE IN TROGLOCEPHALUS-RHINOBATIDIS, NEOHETEROCOTYLE-RHINOBATIDIS AND MERIZOCOTYLE-AUSTRALENSIS (PLATYHELMINTHES, MONOGENEA, MONOPISTHOCOTYLEA, MONOCOTYLIDAE)

The ultrastructural events of spermiogenesis and the ultrastructure of mature sperm of 3 species of monocotylid monogeneans are described. T wo of these species, Troglocephalus rhinobatidis and Neoheterocotyle r hinobatidis are extremely similar in all the aspects studied, and thei r placement in separate subfamilies is questioned. Evidence is present ed in both species for extensive distalward movement during spermiogen esis of an ornamented region associated with cortical microtubules, or iginally located in the zone of differentiation. Spermatids of Merizoc otyle australis lack this ornamentation and the mature sperm also lack s cortical microtubules. Troglocephalus rhinobatidis exhibits the high est number (128) of spermatids in an isogenic group recorded for a fla tworm to date. Sperm of all 3 species have 2 normal axonemes, shifted slightly relative to one another. Comparative data are presented on sp erm and spermiogenesis of all monocotylids examined to date and the ph ylogenetic implications are discussed. (C) 1997 Australian Society for Parasitology. Published by Elsevier Science Ltd.