Author: Müller and Henle, 1837
Body moderately slender. Head very broad and flattened but not trowel-shaped; snout broadly rounded or almost wedge-shaped in dorsoventral view and very short, with preoral length subequal to internarial space and much less than mouth width; eyes fairly small, usually with posterior notches; spiracles usually absent, or present as minute pore- or slitlike openings; no papillose gillrakers on internal gill openings; nostrils small, internarial space about 3 times the nostril width; anterior nasal flaps slightly elongated, distally truncated, and forming distinct tubes with the mesonarial flaps; labial furrows very short, essentially confined to mouth corners, with uppers shorter than lowers and with their ends falling far behind eyes; teeth similar in upper and lower jaws; anteroposteriors in both jaws with erect to semioblique, narrow cusps, strong, high proximal and distal cusplets, but no blades or serrations; cusps of lower teeth not protruding when mouth is closed; 42 to 50/42 to 48 rows of teeth. Interdorsal ridge absent; no lateral keels on caudal peduncle; upper precaudal pit transverse and crescentic. First dorsal origin well behind pectoral free rear tips, its midbase much closer to pelvic bases than pectorals and free rear tip slightly anterior, over, or slightly posterior to pelvic fin origins; second dorsal fin very large but distinctly smaller than first, its height 1/2 to 3/4 of first dorsal height; its origin about opposite or slightly anterior or posterior to anal origin; pectorals fin fairly broad and triangular, their lengths from origin to free rear tip between 3/ 5 to 2/3 of pectoral anterior margins; pectoral origins varying from under interspace between fourth and fifth gill slits to about under fifth gill slits; anal fin about as large as second dorsal, with short preanal ridges and a deeply notched posterior margin. Colour grey or brownish above, without a colour pattern other than variable dusky spots and brilliant white fin tips. Moderate-sized sharks, adults possibly reaching 2.2 m.
This genus has often been placed in the Triakidae but is clearly referable to the Carcharhinidae (see Compagno, 1973c, 1979 for discussion). The genus is reviewed in Taniuchi (1975), Randall (1977) and Compagno (1979).
Previous workers have often recognized two species of Triaenodon, T. obesus (Rüppell, 1837) and T. obtusus Day, 1878. Both Randall (1977) and the writer (1979) tentatively accepted the validity of T. obtusus but were unableto examined its holotype at the time. In 1982 the writer studied the holotype and only specimen, ZSI 2277, 48 cm male, a skin in alcohol in the Zoological Survey of India, Calcutta. This proved to be a full-term fetus, with erupting denticles and an umbilical scar, that is probably referable to Carcharhinus amboinensis, but which had been confused with Triaenodon because its very first erupting series of teeth somewhat resemble Triaenodon teeth in having a simple cusp and a pair of cusplets. However, by peeling back the dental membrane in each jaw the writer observed the transition of this series to typical broad, triangular, heavily-serrated, amboinensis teeth along each tooth row. The tooth row count of this specimen is 27/25, well in the range of C. amboinensis, and its tooth morphology, very short, bluntly rounded snout, short, triangular, non-tubular anterior nasal flaps, lack of an interdorsal ridge, anteriorly situated first dorsal fin with origin over or slightly anterior to the pectoral insertions, very small second dorsal fin with nearly straight posterior margin, deeply notched anal fin, and small eyes fit that species. The writer was able to directly compare the holotype of Triaenodon obtusus with Indian specimens of Carcharhinus leucas and Glyphis gangeticus and found it to be not identical to these species. Hence Triaenodon obtusus is removed from this genus and placed in synonymy of Carcharhinus amboinensis.