are immediately followed by larger spiracles with prominently raised, smooth rims. The nostrils are small and placed close together, and between them is a curtain of skin that overlaps the mouth. The protrusible mouth forms a short, transverse line and is surrounded by a deep groove. There are fewer than 25 tooth rows in each jaw, arranged into bands; the teeth are small with oval bases and pointed crowns. Five pairs of short gill slits are located on the underside of the disc. The pelvic fins are large and broad with convex margins, and originate beneath the pectoral fins; adult males have stubby claspers that do not extend past the pelvic fin margins. The tail is short and thick, with a fold of skin along either side. There is a single rounded dorsal fin positioned behind the pelvic fins. The large caudal fin is nearly symmetrical above and below the caudal peduncle and has rounded corners. The skin is soft and lacks dermal denticles. The Japanese sleeper ray is reddish to chocolate brown above and paler brown below; some individuals are plain, while others have dark or light spots over their dorsal (rarely also ventral) surfaces. The maximum known length of this species is . Distribution and habitat The Japanese sleeper ray inhabits continental shelf waters in the northwestern Pacific Ocean, from southern Japan and Korea to southeastern China and Taiwan. This common, bottom-dwelling species can be found in sandy areas, often near rocky reefs, both close to and far from shore. Off the Izu Peninsula, it has been reported from in depth. Biology and ecology Fairly inactive in nature, the Japanese sleeper ray spends much of its time lying buried on the sea floor. It can produce an electric shock of 30–80 volts to ward off predators, which include the blotchy swell shark (Cephaloscyllium umbratile). Its electric organs are composed of electrocytes, which are specialized cells derived from muscle fibers that are filled with a jelly-like substance. These electrocytes are stacked in vertical columns, with many columns making up each electric organ; this arrangement functions essentially like batteries connected in parallel. The diet of the Japanese sleeper ray includes benthic invertebrates. A parasite of this species is the tapeworm Anteropora japonica (Yamaguti, 1934) Subhapradha, 1955. The Japanese sleeper ray is viviparous, with the developing embryos nourished initially by yolk and later by histotroph ("uterine milk") produced by the mother.