Smoothbelly Catshark

Reaching a length of 59 cm (23 in), the longhead catshark has a soft, very thin body and a long head comprising one-quarter of its total length. The flattened, bell-shaped snout measures roughly 12% of the total length and narrows considerably in front of the nostrils. The oblique nostrils are divided into large, oval incurrent and excurrent openings by triangular flaps of skin on their anterior rims. The small, horizontally oval eyes are somewhat upward-facing, and equipped with rudimentary nictitating membranes. Behind each eye is a modest spiracle. The mouth forms a short, wide arch, with well-developed furrows around the corners. The teeth number 36–44 rows in the upper jaw and over 45 rows in either jaw; each tooth is well-spaced from the next and has three or five cusps, with the central cusp much longer than the others. The five pairs of gill slits are short, with the fourth and fifth pairs over the base of the pectoral fins. The first dorsal fin has a rounded apex and located over the latter third of the pelvic fin bases. The second dorsal fin is similar in shape but much larger than the first, and located over the latter half of the anal fin base. The pectoral fins are moderately large and broad. The medium-sized, rounded pelvic fins are placed fairly close to the pectoral fins. …

Records of the longhead catshark are patchy and widely spread in the Indo-Pacific region: it is known from the East China Sea, southern Japan, the Seychelles, the Philippines, Mozambique, New Caledonia, and northern Australia off Townsville, Ashmore Reef, and North West Cape. This species inhabits the continental slope at depths of 500–1,140 m (1,640–3,740 ft), and is probably found near the sea floor.

The longhead catshark is unique among Apristurus species in that the duodenum is not short, but almost as long as the spiral valve intestine. The function of this trait is unknown, as the feeding habits of this shark have not been documented. The longhead catshark is the only known cartilaginous fish that is normally hermaphroditic: some 85% of the population is functionally male or female, but also possesses undeveloped reproductive organs of the opposite sex (called "rudimentary hermaphroditism"). The factors underlying the evolution of this system have yet to be investigated. This species is oviparous; a single partial egg case has been found, which had tendrils on the posterior corners. Males and females attain sexual maturity at lengths of around 42–49 cm (17–19 in) and 51 cm (20 in) long respectively.