Exostoma Blyth, 1860

Alfred W. Thomson & Lawrence M. Page, 2006, Genera of the Asian Catfish Families Sisoridae and Erethistidae (Teleostei: Siluriformes)., Zootaxa 1345, pp. 1-96 : 65-66

Exostoma Blyth, 1860

Fig. 19

Exostoma Blyth, 1860 : 155. (Type species: Exostoma berdmori Blyth, 1860 , by subsequent designation, by Bleeker (1863: 105). Gender neuter.

Diagnosis: Continuous post-labial groove; gill openings not extending onto venter; homodont dentition; oar-shaped, distally flattened teeth in both jaws; tooth patches separated in upper jaw; 10-11 branched pectoral rays.

Exostoma is distinguished from Glyptosternon , Glaridoglanis , Pareuchiloglanis , Euchiloglanis and Parachiloglanis by having a continuous post-labial groove (Table 5). Exostoma is distinguished from Pseudexostoma and Oreoglanis by having homodont (vs. heterodont) dentition in the lower jaw. It is further distinguished from Oreoglanis by having oar-shaped, distally flattened (vs. pointed) teeth in the upper jaw, and from Pseudexostoma by having homodont (vs. heterodont) teeth in the upper jaw. Exostoma is distinguished from Myersglanis by having tooth patches separated in the upper jaw and oar-shaped, distally flattened teeth in both jaws (vs. tooth patches juxtaposed and pointed teeth in both jaws). Exostoma is further distinguished from Pseudexostoma and Oreoglanis by having 10-11 branched pectoral rays (vs. 16-18).

Description: 6-7 dorsal rays; 10-11 branched pectoral-fin rays; 6 pelvic-fin rays; 5-8 anal-fin rays. Head depressed; snout broadly rounded; body elongate, flattened ventrally to pelvic fins. Eyes minute, dorsal, subcutaneous. Lips thick, fleshy, papillated. Teeth small to large, moveable, oar-shaped, flattened distally and directed posteriorly in distinct patches. Maxillary barbel with well-developed membrane, soft base, and striated pad of adhesive skin. Gill openings narrow, not extending below pectoral-fin base. Branchiostegal membranes confluent with isthmus. Coracoid process not externally visible. No thoracic adhesive apparatus. Paired fins plaited to form an adhesive apparatus.

Distribution: Brahmaputra drainage, northeast India, east and south to the Salween drainages, Myanmar (Kottelat, 1989; Chu et al., 1999; Jayaram, 1999).