Redescription of Scymnodon ichiharai Yano and Tanaka 1984 (Squaliformes: Somniosidae) from the western North Pacific, with comments on the definition of somniosid genera

The somniosid species Scymnodon ichiharai Yano and Tanaka 1984 is redescribed based on the type specimens and additional material from Taiwan and Japan. The range of this species is extended to include Taiwanese waters. Although recently allocated to the genus Zameus, this species is very similar to Scymnodon plunketi from the southern Indo-West Pacific; our molecular evidence indicates that these species are sister-taxa. The genus Proscymnodon Fowler 1934 is placed in the synonymy of Scymnodon Barboza du Bocage and de Brito Capello 1864 and new generic definitions are provided for Scymnodon and the closely related Zameus. The genus Scymnodon is considered to include at least the species S. ichiharai, S. plunketi, and S. ringens; Proscymnodon macracanthus (Regan 1906) is allocated to Scymnodon, but its validity is uncertain. The genus Zameus is considered to be monotypic, containing only the species Z. squamulosus.