Gastromyzon crenastus, H. H. Tan & C. U. M. Leh, 2006

H. H. Tan & C. U. M. Leh, 2006, Three new species of Gastromyzon (Teleostei: Balitoridae) from southern Sarawak., Zootaxa 1126, pp. 1-19 : 9-13

Gastromyzon crenastus , new species

Figs. 3-4

Material examined: BORNEO: SARAWAK (Sadong River basin):

HOLOTYPE: SM uncatalogued, 28.1 mm SL; Serian, Sungai Kuhas, 6.9 km from Tebelu Tebakang turnoff, 5.8 km inside right side road (01º09’10.0”N 110º29’22.7”E); H. H. Tan et al., 5 Sept. 1995.

PARATYPES: SM uncatalogued, 9 ex., 16.9-24.7 mm SL ; ZRC 39416, 10 ex., 16.7-28.4 mm SL ; CMK 11958, 4 ex., 25.1-28.0 mm SL; preceding lots collected with holotype . The following paratype lots are also from the type locality, but with different collectors and dates of collection, as indicated. ZRC 39831, 7 ex., 20.3-29.7 mm SL; H. H Tan et al., 14 Jan. 1996 . ZRC 47075, 6 ex., 18.9-22.4 mm SL; H. H. Tan et al., 19 Feb. 1997 . ZRC 47076, 24 ex., 18.2-26.8 mm SL; Honours 98/99 Fish Group, 23 June 1998 .

NON-TYPE MATERIAL: ZRC 47084, 1 ex., 29.0 mm SL; Sarawak: Tebedu, Sungai Ahi, on road towards Mongkos (00°55.44'N 110°32.34'E); H. H. Tan et al., 12 June 1999 . The following non-type lots are all from the type locality, but with different collectors and dates of collection, as indicated. ZRC 41213, 16 ex., 18.0-22.2 mm SL; H. H Tan et al., 19 Feb. 1997 . ZRC 47077, 2 ex., 19.8-27.8 mm SL; H. H. Tan et al, 29 Oct. 1997 . ZRC 47078, 5 ex., 21.5-24.3 mm SL (site 1, sample 2) ; ZRC 47079, 6 ex., 18.1-26.1 mm SL (site 1, sample 3); Honours 98/99 Fish Group, 24 June 1998 . ZRC 47080, 2 ex., 22.7-25.4 mm SL (site 2, sample 2) ; ZRC 47081, 2 ex., 17.3-23.4 mm SL (site 2, sample 3); Honours 98/99 Fish Group, 25 June 1998 . ZRC 47082, 2 ex., 16.6-16.9 mm SL (site 3, sample 2); Honours 98/99 Fish Group, 26 June 1998 . ZRC 47083, 14 ex., 14.5-24.0 mm SL; H. H. Tan et al., 10 June 1999 . ZRC 47188, 9 ex., 21.4-25.3 mm SL; native collectors, 22 June 2002 .

Diagnosis.- Gastromyzon crenastus differs from its congeners in having the following unique combination of characters: a black body; dorsum with 6-8 thin cream bars or spots; head black, with cream spots and blotches; sublacrymal groove visible from side; absence of a secondary rostrum; absence of a postoral pouch; absence of a subopercular groove; gill slit vertical; snout truncate when viewed dorsally; abdomen without scales; 60-65 scales in lateral line; pelvic fin not overlapping anal fin origin, adpressed dorsal fin not at level overlapping anal fin origin. Maximum size: 29.7 mm SL (ZRC 39831), the smallest known species of Gastromyzon .

Description. General body shape and appearance as in Figs. 3-4. Meristic and morphometric data appear in Table 1. Head truncate in dorsal profile, relatively short (27.5-29.8 % SL) and relatively wide (21.3-24.2 % SL, 74.3-83.3 % HL); head relatively flattened (head depth 12.8-13.9 % SL, 44.3-47.6 % HL); tubercles concentrated at anterior part of snout; snout relatively long (snout length 54.1-58.2 % HL); sublacrymal groove present, distinct when viewed from side; gill slit straight and vertical; length of gill slit about same as eye diameter; subopercular groove absent; postoral pouch absent; belly scales absent; pectoral fin overlapping anterior part of pelvic fin; pelvic fin not overlapping anal fin origin; anteriormost pectoral and pelvic-fin rays with dorsal serrae; dorsal fin situated at about mid body (predorsal length 55.2-59.2 % SL), adpressed dorsal fin not extending past level of anal-fin origin; deepest part of body at dorsal-fin origin (body depth at dorsal-fin origin 16.2-18.5 % SL); anus situated just beyond posterior base of fused pelvic fins; caudal peduncle relatively deep (9.5-10.7 % SL) and relatively short (8.5-10.8 % SL).

Pigmentation and life coloration.-See Fig. 3. Body black on dorsum and sides; dorsum with 6-8 thin cream bars or spots; side with bars interrupted to form spots and blotches; ventrum cream. Head dorsum black, with cream spots and blotches. Eye with golden iris. Dorsal fin light brown, with 1 thick black bar, hyaline interradial membrane and margin; antero-basal black spot present on dorsal fin. Caudal fin base black, fin rays light brown with subdistal part a large black blotch, area just before blotch with iridescent blue, upper border with red, hyaline interradial membrane and thick margin. Anal-fin rays brown, hyaline edge. Pectoral and pelvic fins brown with 1 black bar. Pelvic axillary flap black with distal cream margin.

Color in alcohol.-See Fig. 4. Body black on dorsum and sides, dorsum with 6-8 thin cream bars or spots, side with bars interrupted to form spots and blotches, ventrum cream. Head dorsum black with cream spots and blotches. Dorsal fin rays light brown with 1 thick black bar, fin with hyaline interradial membrane and margin, antero-basal black spot present. Caudal fin base black, anterior part with thin crescentic black band, centre of fin with large black blotch and with thin hyaline margin, hyaline interradial membrane and margin. Anal fin black, with hyaline margin. Pectoral and pelvic fins grey with 1 black bar. Pelvic axillary flap black, with distal cream margin. Juveniles with 5-6 cream spots and blotches on black body, head plain, caudal fin base black, with faint central black bar.

Remarks.- Gastromyzon crenastus can be further differentiated from other congeners of the G. ridens group by the following characters: snout truncate in dorsal profile vs. rounded in G. ridens ; adpressed dorsal fin not overlapping level of anal-fin origin vs. overlapping in G. ridens ; pelvic fin not overlapping anal fin origin vs. overlapping in G. ridens .

Distribution.-This species is known only from the hill streams feeding the Sadong River basin in southern Sarawak (Fig. 7).

Etymology.-The species name is from the Latin crena, meaning notch. This is in reference to the white blotches and bars on the dark coloured body. Used as an adjective.