Comprehensive Description

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Gastromyzon venustus ZBK , new species

Figs. 5-6

Gastromyzon monticola (non Vaillant) - Choy & Chin, 1994: 762.

Material examined: BRUNEI DARUSSALAM ( Temburong district : Temburong River basin): HOLOTYPE : UBD uncatalogued, 38.8 mm SL; Sungai Belalong, in front and near to the Kuala Belalong Field Studies Centre ( 04°32'50.4"N115°09'27.6"E [80 m asl]); H. H. Tan & K. K. P. Lim, 4- 7 Oct 2001 .

PARATYPES : UBD uncatalogued, 3 ex., 37.4-39.6 mm SL ; ZRC 47104, 4 ex., 36.6-49.4 mm SL; same locality as holotype .

NON-TYPE MATERIAL: BRUNEI DARUSSALAM ( Temburong district : Temburong basin): UBD-B- 1b, 1 ex., 39.0 mm SL ; ZRC 38777, 1 ex., 33.7 mm SL; Sungai Temburong, about 1 km downstream of Kuala Belalong; K. K. P. Lim et al., 16 Jun 1995 . UBD-SC /92/7/F5b, 2 ex., 28.1-41.5 mm SL; Sungai Belalong, Kuala Belalong Field Study Centre; S. Choy, 27 Jul 1992 .

Diagnosis. Gastromyzon venustus ZBK differs from its congeners in having the following unique combination of characters: body plain brown, head dorsum plain brown; dorsal, caudal and anal fins red in life; absence of secondary rostrum; absence of postoral pouch; gill slit angular, subopercular groove present and continuous with pectoral-fin origin; a broadly rounded snout when viewed dorsally; presence of sublacrymal groove; absence of scales on abdomen; 58-63 scales in lateral line; pelvic fin just reaching level of anal fin origin, adpressed dorsal fin not overlapping level of anal fin origin. Maximum size: 49.4 mm SL (ZRC 47104).

Description. General body shape and appearance as in Figs. 5-6. Meristic and morphometric data appear in Table 1. Head broadly rounded when viewed dorsally, relatively short (27.5-28.7 % SL) and wide (27.1-28.5 % SL, 95.6-102.8 % HL), head relatively flattened (head depth 12.4-14.5 % SL, 43.7-52.8 % HL). Snout elongated (snout length 63.7-71.7 % HL). Tubercles present over entire snout. Sublacrymal groove present, not visible from side. Gill slit strongly angular. Subopercular groove pronounced and continuous to origin of pectoral fin base. Postoral pouch absent. Scales absent from belly. Posterior part of pectoral fin not overlapping anterior part of pelvic fin in adults, but overlapping in juveniles. Pectoral and pelvic fins with serrae on anteriormost rays. Dorsal fin situated at about mid body (predorsal length 53.9-58.1 % SL). Adpressed dorsal fin not overlapping level of anal fin origin. Deepest part of body at dorsal fin origin (body depth at dorsal fin origin 16.4-18.2 % SL). Anus situated just behind posterior base of fused pelvic fins. Caudal peduncle relatively deep (11.0-11.8 % SL) and long (6.8-10.7 % SL).

Body pigmentation and life coloration. See Fig. 5. Body plain yellowish brown, ventrum cream, a tiny golden spot on posterior edge of every body scale. Head dorsum plain yellowish brown. Eye with golden iris. Dorsal fin red with 3 black bars, the subdistal bar most distinct, with interradial membranes and margin red; and with antero-basal black spot. Caudal fin red with 3-4 black bars, anterior central part gold, subdistal band most distinct, with interradial membranes and margin red. Anal fin reddish, with 2 faint black bars and reddish margin. Pectoral and pelvic fins yellowish brown, with reddish margins. Pelvic axillary flap light yellowish brown. Choy and Chin (1994: 762) noted that small individuals have a blackish-blue spotted appearance, particularly if seen under bright sunlight. The fins have red edges and the caudal fin has 4 dark vertical bands.

Colour in alcohol. See Fig. 6. Body dark brown or black, the ventrum cream. Head dorsum black. Dorsal fin red (when freshly preserved) or brown with 3 black bars, the subdistal bar most distinct, with an antero-basal black spot. Caudal fin red (when freshly preserved) or brown with 3-4 black bars, subdistal bar most distinct, hyaline interradial membrane and margin. Anal fin brown with 2 faint black bars, and a hyaline margin. Pectoral and pelvic fins grey, with reddish to hyaline margin. Pelvic axillary flap brown.

Remarks. In addition to the characters mentioned in the diagnosis, G. venustus ZBK can be further differentiated from other congeners of the G. pariclavis group ZBK by the following characters: plain body pattern (vs. barred body in G. pariclavis ZBK and reticulated body pattern in G. embalohensis ZBK ); fewer transverse scales than G. pariclavis ZBK (11-13.1.10-12 vs. 15-18.1.14-15); greater dorsal depth than G. embalohensis ZBK (19.5-21.7 vs. 18.2-18.9 % SL); greater body depth than G. embalohensis ZBK (16.4-18.2 vs. 14.8-15.7 % SL); dorsal fin base length less than G. pariclavis ZBK (17.1-20.2 vs. 20.1-22.4 % SL).

Distribution. Gastromyzon venustus ZBK is known only from Sungai Belalong, Temburong River basin, Brunei Darussalam (Fig. 7).

Etymology. From the Latin venustus, meaning charming, beautiful. This is in reference to the distinctive life coloration. An adjective.

Field notes. See under G. cranbrooki ZBK for list of syntopic species.


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