Revision of tapeworms (Cestoda: Bothriocephalidea) from lizardfish (Saurida: Synodontidae) from the Indo-Pacific region

Bothriocephalidean cestodes reported from lizardfish (Saurida Valenciennes in Cuvier & Valenciennes) were revised on the basis of newly collected material from type-hosts and available type-and voucher specimens. Instead of nine taxa of four genera listed in the literature, only Oncodiscus sauridae Yamaguti, 1934 and Penetrocephalus ganapattii (Rao, 1954) are considered valid and thus both genera become monotypic. Both taxa are redescribed, including the first scanning electron micrographs and data on intraspecific variability. Both species are unique among bothriocephalid cestodes in the lateral position of the vagina in relation to the cirrus-sac. Oncodiscus sauridae found in Saurida longimanus Norman, S. nebulosa Valenciennes (new host record), S. tumbil (Bloch) and S. undosquamis (Richardson) differs from P. ganapattii found in S. micropectoralis Shindo & Yamanda and S. tumbil in the following characters: (i) scolex shape (fan-shaped, with crenulated bothrial margins in O. sauridae, replaced by a scolex deformatus in P. ganapattii); (ii) site of scolex attachment (in the intestinal lumen in the former taxon versus penetrating through the intestinal wall, and encysted on pyloric caeca in P. ganapattii); (iii) shape of segments (usually only slightly wider than long in O. sauridae versus very short, much wider than long in P. ganapattii); and (iv) number of testes (50-100 per segment in O. sauridae whereas fewer than 60 in P. ganapattii). Bothriocephalus sauridae Ariola, 1900 is considered a species inquirendum, although conspecificity with O. sauridae is very probable. The present study demonstrates the necessity of using standard procedures, especially adequate fixation methods of freshly collected cestode material (hot 4% formaldehyde solution is strongly recommended for morphological studies), because most previous descriptions were based on poor-quality material, including partly macerated worms missing hooklets on the apical disc of the scolex in O. sauridae.