Sunday 30 January 2022

Scyliorhinus hachijoensis: A new species of Catshark from the Izu Islands of Japan.

Catsharks of the genus Scyliorhinus are small, bottom-dwelling Sharks with distinctive mottled colourations found throughout the temperate and tropical regions of the world's oceans, in areas where the seafloor is less than 500 m deep. They can be distinguished from other Catshark species by the presence of a laterally projected flap on the upper lip margin that covers the lower labial furrow, and the presence of a pelvic apron in males. Two species of Scyliorhinus have been reported from Japan Scyliorhinus torazame and Scyliorhinus tokubee (although Scyliorhinus tokubee may be a junior synonym of Scyliorhinus torazame, which is to say an invalid species name given to members of an already established species). Scyliorhinus torazame is found in waters less than 300 m deep off the coast of Japan from Hokkaido to Okinawa, also occurring in South Korea, the East China Sea, and Taiwan. There have been reports of another, undescribed, species of Scyliorhinus being found off the coasts of the islands of Torishima and Mikurajima in waters 450-500 m deep, and having a distinctive colour pattern not seen in any other described species. Despite reports of this unkown species going back at least three decades, with several specimens being kept at the Shimoda Floating Aquarium in Shizuoka, this species has never been formally investigated or described.

In a paper published in the journal Zootaxa on 20 January 2022, Nanami Ito of the Graduate School of Oceanography at Tokai University, Miho Fujii of the Shimoda Floating Aquarium, and Kenji Nohara and Sho Tanaka, also of the Graduate School of Oceanography and of the School of Marine Science and Technology at Tokai University, formally desctibe the deepwater Catshark from the Izu Islands as a new species of Scyliorhinus.

The new species is named Scyliorhinus hachijoensis, meaning 'from Hachijo' in reference to Hachijojima Island, where most of the specimens found were collected (the suffix 'jima' means 'island' in Japanese, but is widely included in English translations which also use 'island' separately). The species is described from 22 specimens caught off the coasts of Hachijojima, Mikurajima, and Torishima islands, at depths of between 100 m and 650 m.

Scyliorhinus hachijoensis, external morphology. (A), (B) NSMT-P 135960, male, 370 mm TL (off the east coast of Hachijojima Island). (C), (D) NSMT-P 135961, female, 322 mm TL (off the east coast of Hachijojima Island). Panels show (A), (C) dorsal and (B), (D) lateral views of the specimens. Scale bar are 30 mm. Ito et al. (2022).

Scyliorhinus hachijoensis specimens range from 29.4 to 41.9 cm in length, and have a generally tapering body shape. The head is broad and the snout short, the eyes large and slit-like. The spiracles (forward gill slits) are just behind the eyes. The first two gill openings are equal in height, with the remaining three progressively smaller in size. The nostrils are broad, the mouth wide, arched, and short. The teeth are similar on both jaws, with 36-49 teeth in the upper jaw and 32-43 in the lower jaw in the specimens examined. 

The pectoral fins are large and rounded, the pelvic fins broadly triangular. The first dorsal fin is sub-rectangular, the second dorsal fin smaller and more triangular. The anal fin is triangular, the caudal (tail) fin narrow-lobed and asymmetrical, with a developed terminal lobe. The male claspers are long and cylindrical. 

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