Pseudexostoma

Pseudexostoma is a genus of catfishes native to Asia.

Taxonomy

Glyptosternum yunnanesis was first described in 1935. However, due to its unique teeth, a separate genus Pseudexostoma was erected in 1979 for this species. The same year, a subspecies of P. yunnanensis was described, P. y. brachysoma. However, it has become apparent that these two groups represent different species. Also, a third species, P. longipterus, was described in 2007.^[1]

Species

There are currently three recognized species in this genus:^[2]

• Pseudexostoma brachysoma X. L. Chu, 1979
• Pseudexostoma longipterus W. Zhou, Y. Yang, X. Li & M. H. Li, 2007
• Pseudexostoma yunnanensis (T. L. Tchang, 1935)

Distribution

Pseudexostoma species are restricted to the upper Salween (Nujiang River) and one upper branch of the Irrawaddy (Dayinjiang) in China. P. brachysoma is known only from the middle and lower Nujiang River. P. longipterus is known only from the middle Nujiang River. P. yunnanensis is only known from the upper Dayinjiang (an upper branch of the Irrawaddy River.^[1] These rivers were once connected, but are now separated. Also, the environment and temperature of the Nujiang River became greatly different between the northern and southern areas, leading to speciation.^[1]

Description

Pseudexostoma species have a continuous groove behind the lip (post-labial groove), gill openings not extending onto the underside (venter), heterodont dentition in both jaws with outer teeth shovel-shaped and sparsely arranged in one or two rows and inner teeth conical and numerous, the tooth patches separated in upper jaw, and 16–18 branched pectoral rays.^[3] The lips are thick, fleshy, and papillated. The paired fins are plaited to form an adhesive apparatus.^[3]

Pseudexostoma species have a moderately compressed body. The head is depressed and broad; it appears triangular from the side and with a rounded snout from above. The eyes are small and ovoid, located at the middle of the dorsal surface of the head. The mouth is transverse and inferior, with the teeth exposed when the mouth is closed. The teeth are embedded in the skin, shovel-shaped, with the tips exposed and arranged in irregular rows. The gill openings are narrow. The dorsal surface is smooth without tubercles. There are four pairs of barbels. The adipose fin base is not connected to the caudal fin. The caudal fin is emarginate with the upper lobe smaller than the lower lobe. The lateral line is midlateral and complete.^[1]

Pseudexostoma species are grey black on the dorsal surface and grey yellow on the ventral region; the caudal fin is grey black with an irregular, small, yellow patch in the middle, and the other fins are grey yellow along the distal edge.^[1] Pseudexostoma grow to about 9.9–15.3 centimetres (3.9–6.0 in) SL.^[4][5][6]

Pseudexostoma species have three notches on the posterior margin of the lower lip. However, in P. yunnanensis, the notches are all the same depth, while in the other two species the middle notch is shallower in depth than the lateral notches. The two median lobes formed by these notches are the same length of the lateral lobes of the lips in P. yunnanensis, but they are longer in the other two species. P. yunnanensis also has more pelvic fin rays (5 vs. 3–4), a shorter adipose fin base, a deeper and longer caudal peduncle, more teeth in the premaxillary tooth band (18–22 vs. 16–18) that are divided into two partially connected patches instead of two isolated patches. Between P. brachysoma and P. longipterus, P. longipterus has longer pectoral fins, pelvic fins, and caudal fins as well as large eyes that are farther apart than in P. brachysoma.^[1]

References