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Author: Springer and Lowe, 1963

Field Marks:
A small, plain Mustelus with fairly low-cusped teeth, a long, acutely pointed snout, very small eyes, broad interorbital space, mostly tricuspidate lateral trunk denticles, and unfringed dorsal fins.

Diagnostic Features:
Body fairly slender. Head moderately long, prepectoral length 19 to 24% of total length; snoutlong and sharply angular in lateral view, preoral snout 6.9 to 10.3% of total length, preorbital snout 6.9 to 9.9% of total length; internarial space broad, 2.7 to 3.8% of total length; eyes small, eye length 2.8 to 3.4 times in preorbital snout and 2.2 to 3.4% of total lenath: interorbital space very broad, 4.5 to 6.3% of total length; mouth moderately long, slightly longer than eye length, 2.3 to 3.6% of total length; upper labial furrows about as long as lowers, upper furrows 0.8 to 1.8% of total length; teeth molariform and asymmetric, with cusp low and blunt or pointed; buccopharyngeal denticles covering anterior half of palate and mouth floor. Interdorsal space 17 to 23% of total length; trailing edges of dorsal fins denticulate, without bare ceratotrichia; first dorsal fairly falcate, its posterior margin nearly vertical from apex, its midbase about equidistant between pectoral and pelvic bases or slightly closer to pectorals; pectoral fins fairly small, length of anterior margins 11 to 14% of total length, width of posterior margin 6.7 to 10% of total length; pelvic fins moderately large, anterior margin length 6.7 to 10% of total length; anal height 2.9 to 4.6% of total length; analcaudal space greater than second dorsal height, 6 to 9.2% of total length; ventral caudal lobe more or less falcate in adults. Crowns of lateral trunk denticles mostly strongly tricuspidate, with longitudinal ridges extending their entire length. Skeleton not hypercalcified in adults; palatoquadrates not subdivided; monospondylous precaudal centra 34 to 39, diplospondylous precaudal centra 43 to 50, precaudal centra 80 to 90. Colour uniform grey or grey-brown, above, light below, no white or dark spots or dark bars. Development viviparous. Size small, adults 43 to 64 cm.

Geographical Distribution:
Western Atlantic: Venezuela to southern Brazil.

Habitat and Biology:
An abundant but localized tropical bottom-dwelling shark of the South American Atlantic continental shelf, occurring close inshore to well offshore, to 101 m depth, on mud, sand and shell bottoms. Occurs in shallow brackish water at the Orinoco River mouth, but not known, to penetrate fresh water. There is at least partial sexual segregation, as catches have been made of considerable numbers of adults all of one sex.

Viviparous, with a yolk-sac placenta, number of young 1 to 7 per litter, most commonly 3 to 5, with sex ratio approximately equal for over 200 embryos sexed. In collections of embryos reported by Springer and Lowe (1963) both small and large embryos occurred during the months of June to September each month, with only a few large embryos taken in November; no seasonality is apparent from available data.

Feeds primarily on crustacea, with occasional individuals taking bony fish, squid, and coelenterates. Manis shrimp were the commonest crustaceans reported by Springer and Lowe (1963), followed by brachyuran crabs, hermit crabs, and shrimp.

Size:
Maximum 64 cm, males maturing at about 43 cm and reaching at least 49 cm, females maturing at about 48 cm and reaching over 58 cm; size at birth between 21 and 24 cm.

Interest to Fisheries:
Probably regularly fished in its range, being very common in some areas; caught mainly with bottom longlines, beam trawls and shrimp seines,and utilized fresh and dried salted for human consumption.

Remarks:
The biology of this species is discussed in Springer and Lowe (1963). This small, broad-headed species is one of the smallest of its genus; it resembles the eastern Pacific M. dorsalis, but differs in its generally lower-cusped teeth, more falcate fins, tricuspidate denticles, and less numerous vertebral centra.

Type material:
Holotype: U.S. National Museum of Natural History, USNM 156930, 480 mm adult male. Type Locality: Northeast of Parimaribo, Surinam, 22 m depth.

Smalleye smooth-hound (Mustelus higmani)