A revision of Megalonchos Baer & Euzet, 1962 (Tetraphyllidea: Onchobothriidae), with the description of two new species and transfer of two species to Biloculuncus Nasin, Caira & Euzet, 1997.

The onchobothriid tapeworm genus Megalonchos Baer & Euzet, 1962 is revised and the generic diagnosis amended based on the examination of some of Southwell's material of M. mandleyi (Southwell, 1927) Baer & Euzet, 1962, the type-specimens of M. dubius Prudhoe, 1969 and M. musteli Prudhoe, 1969, and material of two new species, M. sumansinghai n. sp. and M. shawae n. sp., collected from the snaggletooth shark Hemipristis elongatus off northern Australia. Based on their possession of two pairs of uni-pronged hooks (rather than one pair of bi-pronged hooks) and possession of, rather than lack of, post-vaginal testes, M. dubius and M. musteli are transferred to Biloculuncus Nasin, Caira & Euzet, 1997 as B. dubius (Prudhoe, 1969) n. comb. and B. musteli (Prudhoe, 1969) n. comb. Both new species of Megalonchos differ from M. mandleyi in their possession of conspicuously smaller hooks and shorter cephalic peduncles. The new species are readily distinguished from one another in that, whereas the pores of the axial prongs of the medial and lateral hooks are located well anterior to the middle of the prong in M. sumansinghai n. sp., they are well posterior to the middle of the prongs in M. shawae n. sp. In addition, the base of the lateral hook is longer relative to that of the medial hook in the latter species than it is in the former species. The proglottid anatomy of valid species of Megalonchos is described for the first time, and the lack of post-vaginal testes is confirmed for the genus. In addition, members of this genus appear to be characterised by a sacciform uterus that extends only to the level of the cirrus-sac and an ovary that is H-shaped in frontal view and bilobed in cross-section. Species of Megalonchos have now been reported from two of the eight known species of hemigaleid sharks.