Author: (Quoy and Gaimard, 1824)
Anterior nasal flaps very short, not expanded into barbels; snout moderately long, bulbously conical, length about 2/5 of head length and less than distance from mouth to pectoral origins; gill openings very small, uniformly broad; lips thin, not fringed, pleated or suctorial; teeth strongly different in upper and lower jaws, uppers small, with narrow, acute, erect cusps and no cusplets, not bladelike, lowers much larger, bladelike, interlocked, with a high, broad, nearly erect cusp and distal blade, edges not serrated; tooth rows 21/19-23. Both dorsal fins spineless; first dorsal origin far behind free rear tips of pectoral fins, insertion well ahead of pelvic origins but much closer to pelvic bases than pectorals; second dorsal fin much larger than first, with its base about 4 times as long as base of tiny first dorsal; origin of second dorsal over rear end of pelvic bases; pectoral fins with short, broadly rounded free rear tips and inner margins, not expanded and acute or lobate; caudal fin nearly symmetrical, paddle-shaped, with short, strong upper lobe and long lower lobe, subterminal notch well-developed. No precaudal pits but with low lateral keels on caudal peduncle, no midventral keel. Dermal denticles flat and blocklike, not pedicellate, no posterior cusps on flat, depressed crowns. Cloaca normal, not expanded as a luminous gland. Colour blackish with conspicuously light-edged fins.
Oceanic and amphitemperate. South central Atlantic: Near Ascension Island, east of Fernando di Noronha Island, west of Cape of Good Hope, South Africa. Southern Indian Ocean: Madagascar to Western Australia. Southern central Pacific: Between New Zealand, Phoenix Island and southern Chile. Northern central and eastern Pacific: Midway and Hawaiian Islands to off California (USA).
Habitat and Biology:
This pygmy shark is an epipelagic, mesopelagic, and perhaps bathypelagic inhabitant of the central water masses of the North and South Pacific, South Atlantic, and southern Indian Ocean, with water depths from 1829 to 9938 m. It occurs at or near the surface at night and apparently descends to at least midwater depths, to probably well below 300 m during the day; sand grains in the stomach of one specimen suggests that it may have been feeding on the bottom, presumably below 1800 m depth. All known specimens have been caught at the surface at night while none have been taken in midwater trawls at night or during the day. This also suggests that the diel vertical migrations of this little shark are enormous, at least 1500 or more metres each way to put it below the normal range of midwater trawl hauls in the day. In human terms this would be roughly equivalent to someone climbing at least 11 km up and down each day. Development ovoviviparous, with 8 young per litter. This shark eats deepwater squid and bony fishes with some crustaceans, but apparently does not take prey as relatively large as the squid taken by Isistius brasiliensis.
Maximum total length 27 cm, males maturing between 17 to 19 cm and reaching 22 cm, females maturing between 22 and 23 cm and reaching 27 cm; size at birth greater than 6 cm and less than or about 10 cm.
Interest to Fisheries: None.
Holotype: Museum National d'Histoire Naturelle, Paris, MNHN 1216, 196 mm male. Type Locality: Mauritius, Indian Ocean.