The status of the genera Hysterolecithoides Yamaguti, 1934, Neotheletrum Gibson & Bray, 1979 and Machidatrema Leon-Regagnon, 1998 (Digenea : Hemiuroidea), including a description of M-leonae n. sp from Australian waters

A diagnosis is given for the lecithasterid genus Hysterolecithoides Yamagut i, 1934, which is now found to have two to six (possibly seven) vitelline m asses. The species H. frontilatus (Manter, 1969) is returned to the genus, having been considered a member of the bunocotylid genus Neotheletrum by re cent authors. It is redescribed from Siganus nebulosus, Moreton Bay, and S. doliatus, Lizard Island, Great Barrier Reef and New Caledonia, with emphas is on the presence of Juel's organ, a uterine seminal receptacle and the bl ind sac associated with the genital atrium. It differs from its congeners i n the trajectory of the pars prostatica which recurves dorsally to the sinu s-sac. Oligolecithoides Shen, 1982 is synonymised with Hysterolecithoides a nd O. trilobatus Shen, 1982 is synomised with H. epinepheli Yamaguti, 1934. Machidatrema Leon-Regagnon, 1998 is diagnosed, and found to be close to Hy sterolecithoides, but differs in the lack of a blind-sac projecting from th e dorsal genital atrium, by its tandem testes, the coiling of the uterus be tween the testes and the ovary, and the ventral excretory pore. M. leonae n . sp. is described from Siganus fuscescens, S. lineatus, S. doliatus, S. co rallinus, S. vulpinus and Scarus globiceps at Heron Island, Queensland. It differs from its closest congener, M. akeh, in the muscular and tegumental flap over the genital pore and details of the terminal genitalia. M. chilos toma (Machida, 1980) and M. kyphosi (Yamaguti, 1970) are redescribed from K yphosus vaigiensis from Heron Island. Neotheletrum Gibson & Bray, 1979 is d iagnosed: it differs from Hysterolecithoides in its confluent excretory arm s, blind seminal receptacle (no Juel's organ) and uniformly tripartite vite llarium. A cladistic analysis suggests that M. chilostoma and M. kyphosi ar e not best accommodated in Machidatrema, that Machidatrema (sensu stricto) is monophyletic and that Hysterolecithoides is paraphyletic. Hysterolecitho ides and Machidatrema are considered hysterolecithine lecithasterids, whils t Neotheletrum is retained as an opisthadenine bunocotylid.