Phallostethus cuulong

description

Description. Counts of the holotype are asterisked, and the frequency of each count is given in parentheses following the relevant count. Dorsal-fin rays 7 (2), 8 * (6) or 9 (1); anal-fin rays 24 * (4), 25 (1), 26 (3) or 27 (1); pectoral-fin rays 11 (2), 12 * (7) or 13 * (9); scales in lateral series 34 (5), 35 * (10) or 36 (3); predorsal scales 1 + 25 (1), 2 + 25 (1), 2 + 26 (4) or 2 + 27 * (3); transverse scales 6 (3), 7 * (12) or 8 * (3); circumpeduncular scales 12 * (8) or 13 (1); paradentary teeth approximately 5 (1), 6 (3), 7 (3), 8 (3), 10 (1), 13 * (1), 14 (2), 15 * (1), 18 (2) or 19 (1). The following measurements are % of SL: head length 22.1 – 24.1; snout length 7.0 – 8.5; eye diameter 6.7 – 7.3; interorbital width 3.3 – 5.2; length of jaw 8.0 – 9.4; predorsal length 78.0 – 82.6; preanal length 46.4 – 48.7; maximum body depth 15.0 – 18.7; body depth at anal-fin origin 12.4 – 15.0; body width 9.4 – 14.0; caudal-peduncle length 18.6 – 20.7; caudal-peduncle depth 5.6 – 7.6; length of dorsal-fin base 9.1 – 10.5; length of anal-fin base 32.3 – 36.7; pectoral-fin length 14.6 – 19.1; caudal-fin length 20.1 – 22.4. Head depressed anteriorly, with flat or barely concave interorbi

Phallostethus cuulong, a new species of priapiumfish (Actinopterygii: Atheriniformes: Phallostethidae) from the Vietnamese Mekong

diagnosis

Diagnosis. Phallostethus cuulong is distinguished from congeners in having following characters: seven serrae on the second ctenactinium in adult males (vs. five and eight in P. dunckeri and P. l e h i, respectively); 11 – 13 pectoral-fin rays (vs. 9 – 10 and 12 in P. dunckeri and P. l e h i, respectively); 11 – 14 + 25 - 26 = 37 – 40 vertebrae (vs. 13 + 27 = 40 and 12 + 28 = 40 in P. dunckeri and P. l e h i); approximately 5 – 19 teeth on paradentary (vs. 15 – 20 and 28 or more in P. dunckeri and P. le h i, respectively). All six examined males are dextral (vs. one and two known males of P. dunckeri are sinistral and dextral respectively, and all four know males of P. l e h i are sinistral).

Phallostethus cuulong, a new species of priapiumfish (Actinopterygii: Atheriniformes: Phallostethidae) from the Vietnamese Mekong

discussion

Remarks. Following the key to genera of phallostethid fishes by Parenti (1989), the new species is clearly assigned to Phallostethus by having the combination of, e. g., shield-like pulvinulus, large seminal papilla, long toxactinium, membranous dome on dorsal surface of head, 24 – 27 anal-fin rays, 37 – 40 vertebrae, serrated ctenactinium, non-projecting lower jaw beyond upper jaw, no first dorsal fin, and 7 – 9 second dorsal-fin rays. In particular, no other phallostethid genera are known that bear 24 or more anal-fin rays (vs. 22 or less anal-fin rays in the other phallostethids). Within the genus, the new species resembles the Bornean species Phallostethus lehi in sharing 11 – 13 pectoral-fin rays, but differs in having seven serrae on second ctenactinium in adult (vs. eight in P. l e h i), 25 – 26 caudal vertebrae (vs. 28), and 6 – 19 paradentary teeth (vs. 28 or more). All six examined males of the new species are dextral, immediately distinguishing them from sinistral males in P. l e h i. The new species is also distinguished from Phallostethus dunckeri, known only from Johor, Malay Peninsula but presumed to be extinct (Parenti, 1996), by having seven serrae on second ctenac

Phallostethus cuulong, a new species of priapiumfish (Actinopterygii: Atheriniformes: Phallostethidae) from the Vietnamese Mekong

distribution

Distribution, habitat and the other notes. Phallostethus cuulong is known from nine specimens, six males and three females, collected from shallow waters (<1.2 m depth) around banks of slow-flowing turbid canals and rivers with soft muddy bottoms in Soc Trang and Tra Vinh Provinces, Vietnam. The first author (KS) observed that a fish, latter designated as one of the paratypes of Phallostethus cuulong (NSMT-P 106665), swam slowly at the water surface around a bank of the slow-flowing tidal canal with dense semi-aquatic vegetation. A bright white blotch on dorsal surface of head was clearly confirmed in the field, but less vivid than that of the sympatric aplocheilid, Aplocheilus panchax (well-known for its reflective “ pineal ” spot on the top of the head). When the fish was disturbed, it quickly swam a short distance away from the original position; it was subsequently scooped up carefully using a hand net by KS. The species was usually solitary, and collected by hand nets or seine nets. Like the other phallostethids in the Vietnamese Mekong, this species has never been seen in the fish markets. As far as we aware, all fishes of the family Phallostethidae have no vernacular names i

Phallostethus cuulong, a new species of priapiumfish (Actinopterygii: Atheriniformes: Phallostethidae) from the Vietnamese Mekong