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Author: Bigelow and Schroeder, 1944

Field Marks:
An Apristurus with a slender body, broad internarial, large gill slits, long anteriorly expanded mouth, first dorsal fin half area of second, moderately high and angular anal fin, narrow caudal fin, dark coloration with unmarked fins.

Diagnostic Features:
Body relatively slender, trunk slightly tapering toward head. Snout moderately long, rather narrow, and bell-shaped, preoral snout about 7 to 10% of total length; gill slits large, the longest 2/3 to slightly greater than eye length; gill septa without projecting medial lobes or pleats, but well-incised; eyes small in adults, about 3 to 4% of total length; nostrils narrow, their width about 1.4 to 1.7 times in internarial space; incurrent and excurrent apertures broadly oval, anterior nasal flaps high and angular; mouth long (especially in adult males), large, and broadly arched, with dental bands prominently expanded and with lower ones falling well behind uppers; mouth and labial furrows extending well in front of eyes; labial folds somewhat enlarged, with lower diagonal to nearly transverse to body axis; mouth and teeth greatly enlarged in males. Interdorsal space almost or quite twice first dorsal base, half to two-thirds of preorbital snout; first dorsal fin half area of second or less, base of first about two-thirds the length of second; origin of first dorsal over rear half of pelvic bases; second dorsal insertion over or in front of anal insertion; pectoral fins rather small, anterior margins about 10 to 12% of total length; inner margins moderately long, half to twothirds length of pectoral bases; interspace between pectoral and pelvic bases moderately short, somewhat less than preorbital length and about 9 to 12% of total length in adults; pelvic fins fairly low and rounded or subangular; anal fin fairly long, moderately high, and angular, about four times as long as high, base slightly less than or greater than prespiracular space and 13 to 16% of total length in adults; caudal fin narrow, without a developed crest of enlarged denticles on dorsal caudal margin, though denticles there are slightly enlarged. Lateral trunk denticles of body with crowns close-set and partly erect, giving the skin surface a feltlike or fuzzy texture. Colour dark brown, without conspicuous markings. Adults small, to 48 cm.

Geographical Distribution:
Western North Atlantic: Cuba, northern Gulf of Mexico, Panama.

Habitat and Biology:
An uncommon catshark of the western Atlantic continental slopes on or near bottom at 860 to 1098 m depth. Oviparous, with one egg per oviduct laid at a time. This shark has sexual dimorphism unusually well-developed in adults, with the males having much larger conical teeth without cusplets (cusplets present in females) and much longer and wider mouths and jaws than females. Springer (1979) interpreted this as a male adaption for grasping females in courtship and copulation, and suggested that the enlarged conical teeth of males would do less damage than smaller teeth with cusplets. It is uncertain, however, why one species of Apristurus has sexual heterodonty (and 'heterognathy') so strongly developed, while others that may live in the same habitat alongside it do not.

Size:
Maximum 46 cm, adult males 43 to 46 cm, adult females 40 to 41 cm.

Interest to Fisheries:
None.

Type material:
Holotype: Museum of Comparative Zoology, Harvard, MCZ 36092, 407 mm female. Type Locality: North coast of Cuba, 23° 24'N, 80° 44'W, western North Atlantic, at 1061 m.

Broadgill catshark (Apristurus riveri)