Author: Smith, 1913
One of the smallest living sharks, not exceeding 24 cm, with anal fin and two equal-sized, spineless dorsal fins, first dorsal fin over abdomen and slightly closer to pelvic fins than pectorals, preoral snout less than 1.5 times mouth length, nictitating eyelids, a triangular mouth, labial furrows rudimentary or absent, comblike posterior teeth, short anterior nasal flaps that do not reach mouth, no nasoral grooves or barbels, a long, narrow, ribbonlike caudal fin with prominent dark banding, and brown coloration.
Preoral snout less than 1.5 times mouth length; labial furrows rudimentary or absent. Dorsal fins fairly large and high, with anterior margin of first dorsal at a low angle to body axis; anal fin height less than half dorsal heiohts: iunction of ureventral and postventral caudal margins broadly rounded. Laterai trunk denticles narrow crowned and with long, narrow cusps. Colour brown, with prominent dark banding on tail and dark markings on dorsal fins.
Wideranging in the Indo-West Pacific, but with 4 spotty records from Tanzania, the Gulf of Aden, India (Gulf of Mannar, Bay of Bengal), 3 the Andaman Islands, Viet Nam, and the Philippines. The immense range of this: species is striking compared to the limited ranges of other members of the genus Eridacnis.
Habitat and Biology:
A deepwater tropical benthic shark that often occurs on mud bottoms, on the upper continental and insular slopes and the outer shelves at depths from 71 to 766 m. In some areas where it occurs (particularly southern India and the Philippines), the pygmy ribbontail shark is very common.
Ovoviviparous, number of young 1 or 2 in a litter. Fetuses resorb their yolk sacs and are ready for birth at about 10.1 to 10.7 cm length. This shark is extraordinary in the great size of full-term young compared to their mothers, and the small size of females at maturity. Examination of females in Indian waters show that these may become pregnant at 16.6 cm length or less (large eggs appear at about 15 cm). It is possible that females grow considerably while pregnant, as only the larger females above 18 cm have large, near or full-term young, while small females below 17 cm only have embryos in earlier stages.
Feeds primarily on small bony fishes and crustaceans, with squid a lesser component of its diet. In the stomachs of over 300 specimens from Indian waters bony fishes, particularly lanternfishes but also bristlemouths (Gonostomatidae), small eels and digested fish remains formed about 55% of this shark's diet by volume; crustaceans, primarily deepwater shrimp but also stomatopods and crab larvae occurred at 28% by volume; squid occurred at about 14% by volume, but few other items were recorded (bivalves in one stomach).
Maximum 24 cm; males mature at 18 to 19 cm or less, and reach 23 cm; females mature at about 15 to 16 cm and reach 24 cm; size at birth about 11 cm. This is one of the two smallest living sharks known at present, and is only rivalled in size by the squaloid Squaliolus laticaudus.
Interest to Fisheries:
Minimal, taken in commercial bottom trawls in the Philippines, but utilization there is not known.
The writer examined the holotype of Proscyllium alcocki Misra, 1947 (ZSI F 229/1, a 208 mm adult male) in the collections of the Zoological Survey of India, Calcutta, and was able to confirm the synonymy of Misra's species with Eridacnis radcliffei.
Holotype: U.S. National Museum of Natural History, USNM-74604, 230 mm adult female. Type Locality: Off Jolo Light, Jolo Island, Sulu Archipelago, The Philippines, 6°11.8'N, 121°08.3'E, 295 m depth.