Revision of the family Sphyriocephalidae Pintner, 1913 (Cestoda: Trypanorhyncha), with the description of Heterosphyriocephalus encarnae n. sp. and redescriptions of two species of Sphyriocephalus

The family Sphyriocephalidae Pintner, 1913, which comprises the genera Hepatoxylon Bosc, 1811, Sphyriocephalus Pintner, 1913 and Heterosphyriocephalus Palm, 2004, is revised from newly-collected and museum material. Heterosphyriocephalus encarnae n. sp. is described from the pelagic thresher, Alopias pelagicus Nakamura (Lamniformes: Alopiidae) collected from the Pacific Ocean off Boca del Alamo, Mexico. This species can be readily distinguished from the rest of sphyriocephalids by its small size, low number of proglottids and long velum with a characteristically irregular and folded border, among other features. The tentacles show a distinctive basal armature, and a heteroacanthous typical metabasal armature with heteromorphous hooks. Redescriptions are provided for Sphyriocephalus tergestinus Pintner, 1913 and S. viridis (Wagener, 1854) Pintner 1913 based on novel morphological data. A phylogenetic analysis including the available sequences of sphyriocephalid species plus new generated sequences of S. tergestinus has been performed, from which S. tergestinus is allocated into Heterosphyriocephalus as H. tergestinus n. comb. New dichotomous keys for the determination of genera of Sphyriocephalidae are provided, as well as new generic diagnoses for Sphyriocephalus and Heterosphyriocephalus and keys for the determination of species within both genera. Although the morphology of the genus Hepatoxylon is not addressed in the present study, the available sequence of the type-species has been incorporated in the phylogenetic analysis and its relationship to the other two genera of the family is discussed.