Author: Hasse, 1879
Field Marks:
Small to moderate-sized sharks with horizontally oval eyes, internal nictitating eyelids, no nasoral grooves or barbels, small spiracles, a short to long, arched mouth that reaches past anterior ends of eyes, moderately long labial furrows, small to moderately large bladelike teeth in the upper jaw, more or less cuspidate teeth in the lower jaw, two moderate-sized spineless dorsal fins and an anal fin, the first dorsal base well ahead of pelvic bases, the second dorsal fin about 2/3 as large as first, precaudal pits present, caudal fin with a strong ventral lobe and lateral undulations on its dorsal margin, intestine with a spiral valve, and usually no colour pattern.
Diagnostic Features:
Head without laterally expanded blades; eyes horizontally oval, with lengths 1.1 to 1.9 times the height; nictitating eyelids internal; spiracles present and small anterior nasal flaps lobular and short, not barbel-like; internarial width about 1.9 to 3 times the nostril width; labial furrows moderately long; teeth small to large, with acute and narrow to moderately broad cusps, lateral cusplets; basal ledges and grooves strong to vestigial; teeth strongly differentiated in upper and lower jaws, uppers compressed and bladelike, lowers cuspidate and not compressed; posterior teeth not comblike; tooth rows 25 to 36/28 to 43. Precaudal pits present. First dorsal fin moderately large and not keel-like, much shorter than caudal fin; first dorsal base well ahead of pelvic bases, equidistant between pectoral and pelvic bases or slightly closer to pectoral bases than to pelvics; midpoint of first dorsal base always in front of pelvic origins; pectoral fins with radials extending into distal web of fins. Ventral caudal lobe strong, undulations or ripples present in dorsal caudal margin. Neurocranium without supraorbital crests; vertebral centra with strong, wedge-shaped intermedial calcifications. Valvular intestine with a spiral valve of 4 to 6 turns. Colour usually uniform greyish, sometimes with horizohtal stripes. Development viviparous.
Habitat, Distribution and Biology:
The Hemigaleidae is a small family of common coastal tropical sharks of continental and insular shelf waters down to 100 m depth but usually in shoaler water. Although formerly of worldwide distribution, they currently are limited to the eastern Atlantic and continental Indo-West Pacific but not extending far into the central Pacific. Most of the approximately 7 species are small, and attain a length of 1.4 m or less, but the snaggletooth shark (Hemipristis elonuatus) reaches about 2.3 to 2.4 m. The family is closely related to, and is a sister family of the Carcharhinidae, but is readily distinguishable.
Hemigaleids feed on a variety of small bony fishes, small elasmobranchs, cephalopods, crustaceans, and echinoderms. At least two species of small weasel sharks (Paragaleus pectoralis and Hemigaleus microstoma) specialize on a largely cephalopod diet and have small, short mouths, rather weak flat jaws, small upper cutting teeth and small erect lower teeth; while the largely fish-eating Hemipristis elongatus has a long mouth, powerful jaws, large, serrated upper teeth and long curved lower teeth. These structural differences may reflect differences in feeding behaviour between the cephalopod specialists and fish-eaters of this family. The shortened mouths of the cephalopod feeders could enhance suction feeding at the expense of grabbing and impaling ability, which may be more effective against squid, cuttlefish and octopi; the rather small teeth of the cephalopod specialists may be adequate for holding and dismembering such soft, slippery prey. Conversely, the elongated mouth and impressive, rather mako-like teeth of the snaggletooth shark (and possibly also the hooktooth shark, Chaenogaleus macrostoma, with similar jaws and teeth) may be more effective against fish victims, in grabbing, impaling and slicing them after a chase. The snaggletooth shark (and the hooktooth) has much larger gill slits than the two known cephalopod specialists, and may be a more active swimmer; the short gill slits of the cephalopod eaters may be helpful in limiting backflow into the pharynx during suction feeding.
These sharks are not known to have attacked people, and for the most part are probably harmless; however, the snaggletooth shark is sufficiently large and powerfully armed to be considered at least potentially dangerous.
Interest to Fisheries:
Members of this family are common catches in artisanal and small commercial inshore and near offshore fisheries where they occur, in the eastern Atlantic and Indo-West Pacific. They are utilized primarily for human consumption, but fins of the larger species may be used by the oriental sharkfin trade and liver oil for vitamins. They are however, of modest importance in such fisheries, as they are greatly outnumbered by various species of the Carcharhinidae and Sphyrnidae where they occur.
Remarks:
The present arrangement of the Hemigaleidae follows Compagno (1979). Genera in this family have conventionally been placed in the Carcharhinidae.