New species of Crossobothrium (Cestoda: Tetraphyllidea) from the broadnose sevengill shark, Notorynchus cepedianus, in Argentina.

Two new species of Crossobothrium were found inhabiting Notorynchus cepedianu s, the broadnose sevengill shark, collected from the coast of Buenos Aires Province, Argentina. Crossobothrium antonioi n. sp. is the smallest species in the genus and has at least 3 times as many testes per mature proglottid than any other congener. It can be further distinguished from other species of Crossobothrium by the possession of crenulated bothridial margins and a different microthrix pattern. Crossobothrium pequeae n. sp. is distinguished from all other species in the genus using the following combination of characters: worm size, number of testes per mature proglottid, bothridial margins, microthrix pattern, and the extension of ovary and testicular fields in cross section. Species in Crossobothrium, with the exception of C. laciniatum , seem to be restricted to hexanchid sharks, and a single species of shark can be parasitized by multiple species of Crossobothrium, as is the case with N. cepedianus, and probably Hexanchus griseus.