Author: Garman, 1913
Field Marks:
A fairly stocky Mustelus with a very long head and long, angular, acutely pointed snout, very small eyes, broadly rounded tooth crowns, short caudal peduncle, relatively few precaudal vertebral centra, 58 to 63, and, at least in young and preadolescents, vertical dark bars on the body.
Diagnostic Features:
Body fairly stout. Head very long, prepectoral length 22 to 24.5% of total length; snout very long and angular in lateral view, preoral snout 8 to 9% of total length, preorbital snout 9.4 to 10.2% of total length; internarial space broad, 2.9 to 3.4% of total lenuth; eyes small. eve length 3.8 to 4.3 times (laroest juveniles at about 62 cm have it over 4) in preorbital snout and 1.9 to 2.5% of total length; interorbital space broad, 4.8 to 5.2% of total length; mouth long, greater than eye length and 3.4 to 4.2% of total length; upper labial furrows considerably longer than lowers, upper furrows 2 to 2.4% of total length; teeth molariform and symmetrical, with cusp and cusplets absent and crown broadly rounded; buccopharyngeal denticles covering most of palate and floor of mouth except medial rear third. Interdorsal space 16 to 19% of total length; trailing edges of dorsal fins denticulate, without bare ceratotrichia; first dorsal broadly triangular, with posteroventrally sloping posterior margin, midbase closer to pelvic bases than pectorals; pectoral fins moderate-sized, length of anterior margins 13 to 15% of total length, width of posterior margins 11 to 13% of total length; pelvic fins large, anterior margin length 7.4 to 9.2% of total length; anal height 2.8 to 3.2% of total length; anal-caudal space shorter than second dorsal height, 4.2 to 5.6% of total length; ventral caudal lobe hardly developed in large juveniles. Crowns of lateral trunk denticles lanceolate, without longitudinal ridges or when present extending up to only half of their length. Skeleton not hypercalcified in large juveniles; palatoquadrates not subdivided; monospondylous precaudal centra 32 to 35, diplospondylous precaudal centra 23 to 30, precaudal centra 58 to 63. Colour grey or grey-brown, above, light below, no white or dark spots but with dark vertical bars on at least young and juveniles. Development unknown. Size large, adults above 62 cm.
Geographical Distribution:
Western South Atlantic: Southern Brazil to northern Argentina.
Habitat and Biology:
A little-known temperate-water inshore bottomdwelling shark of the Atlantic South American continental shelf. Livebearing, but mode of reproduction unknown. Presumably eats crustaceans and other bottom-dwelling invertebrates.
Size:
Maximum size probably between 1 and 1.5 m; size at maturity for males above 62 cm; size at birth at or below about 39 cm.
Interest to Fisheries:
Fished commercially in Uruguay, and probably elsewhere where it occurs, and utilized fresh-frozen and dried salted for human consumption and for its oil.
Remarks:
This is a very distinctive species, closest to M. mento but easily separable by its longer and more angular head.
Type material:
Holotype: Museum of Comparative Zoology, Harvard, MCZ 154, 607 mm immature male. Type Locality: Rio Grande do Sul, Brazil.