A New Species of Acanthobothrium (Cestoda: Onchoproteocephalidea) from the Smalleye Pygmy Shark, Squaliolus aliae (Chondrichthyes: Squaliformes: Dalatiidae), from Taiwan

The cestode fauna of Squaliolus aliae was examined for the first time following the collection of elasmobranch specimens from Taiwan in 2005, 2013, and 2017. This small shark was found to host 2 tapeworm species. These consist of Acanthobothrium katherineae n. sp., which is new to science and is described herein, and a second species, in the genus Scyphophyllidium, which also appears to be new, but which is represented by insufficient material for formal description. Acanthobothrium katherineae is a category 5 species. It can be distinguished from 5 of the 19 other category 5 species in that it is apolytic, retaining proglottids on its strobila until they are gravid. This new species differs from the remaining 14 category 5 species in its combination of the following features: It is a smaller worm, has fewer than 100 proglottids, has a relatively short cephalic peduncle, and differs in bothridial size and loculus ratio. Sequence data for the D1–D3 region of the 28S rDNA gene were generated for one specimen of A. katherineae. This sequence, along with comparable sequence data for adults of 14 described and 2 undescribed species as well as specimens of 6 undescribed larval members of the genus, was included in a maximum likelihood phylogenetic analysis. The resulting tree places the shark-hosted A. katherineae within a clade of stingray-hosted species, with Acanthobothrium romanowi as its sister taxon. Acanthobothrium katherineae is 1 of only 19 Acanthobothrium species known to parasitize sharks. The tree resulting from this study, which is preliminary given the relatively poor taxon sampling of the diversity in the genus, included 3 of the shark-parasitizing Acanthobothrium species and suggests that all 3 represent host-switching events. This is the first report of an Acanthobothrium species from the family Dalatiidae and the first report of a Scyphophyllidium species from the order Squaliformes. These findings suggest that other members of the Squaliformes, many of which have not previously been examined for parasites, may host additional novel cestode taxa.