Exostoma berdmorei Blyth, 1860

Ng, Heok Hee & Vidthayanon, Chavalit, 2014, A review of the glyptosternine catfish genus Exostoma Blyth 1860 from Thailand, with descriptions of two new species (Teleostei: Siluriformes), Zootaxa 3869 (4), pp. 420-434 : 421-423

Exostoma berdmorei Blyth, 1860

( Figs. 1 , 2 )

Exostoma berdmorei Blyth, 1860: 155 (type locality: Tenasserim, Myanmar); Hora & Silas, 1952: 27; Vidthayanon et al., 2005: 106 (text only).

Exostoma labiatum (non M’Clelland)— Day, 1870: 525.

Glyptosternum sp.— Hora, 1923: 43

Material examined. NIFI 0 894 (2), 34.3–54.0 mm SL; Thailand: Mae Hong Son Province, Mae Sariang District, Huay Po. NIFI 1669 (1), 66.4 mm SL; Tak Province, Tha Song Yang District, Mae Jawang. ZRC 54293 (1), 53.4 mm SL; Thailand: Mae Hong Son Province, left side tributary of Mae Nam Pai, about 14 km N of Mae Sariang at bridge with road 108.

Diagnosis. Exostoma berdmorei is distinguished from congeners in having a combination of the following characters: eye diameter 10.1–11.9% HL; head width 18.3–21.1% SL; pectoral-pelvic distance 32.8–36.0% SL; dorsal-to-adipose distance 9.2–11.7% SL; body depth at anus 11.0–12.7% SL; length of adipose-fin base 32.8–35.8% SL; adipose fin adnate to upper procurrent caudal-fin rays; caudal peduncle length 16.4–19.6% SL; caudal peduncle depth 9.2–9.7% SL; weakly forked caudal fin; 22–23 preanal vertebrae.

Description. Morphometric data as in Table 1 . Head and body broad, very strongly depressed, with paired fins greatly enlarged to form elongate ovoid adhesive disc with body. Rostral margin rounded in dorsal view, moderately curved in lateral view. Dorsal profile rising gently and evenly from anterior orbital margin to origin of dorsal fin, then sloping gently ventrally to end of caudal peduncle. Ventral profile flat to anal-fin base, then sloping gently dorsally to end of caudal peduncle. Anus and urogenital openings located at vertical through posterior margin of adpressed pelvic fin. Mouth ventrally directed with broad, thin and papillate lips. Most of premaxillary tooth patches exposed when mouth is closed. Lower lip with prominent labial fold bearing entire posterior margin, notched at insertions of inner mandibular barbels. Postlabial groove on lower jaw present, uninterrupted.

Jaw teeth distally flattened, oar-shaped, in two rounded triangular patches narrowly separated at midline on upper jaw. Teeth on lower jaw situated in two well-separated, roughly triangular patches. Palate edentulous.

Eyes small, dorsolaterally situated, subcutaneous. Gill openings narrow, extending from base of first pectoralfin ray to level immediately dorsal to base of posteriormost pectoral-fin ray.

Barbels in four pairs. Nasal barbel moderately long, reaching to middle of orbit. Maxillary barbel flattened, with flap of skin fringing posterior margin; its tip pointed; ventral surface with numerous striae; extending beyond base of pectoral fin. Inner mandibular barbel slightly flattened, very short; originating from notch on posterior margin of lower lip. Outer mandibular barbel situated lateral to inner mandibular barbel; slightly flattened, reaching to two-thirds of distance between its base and base of first pectoral-fin ray.

Dorsal fin without spine, with i,6 (4) rays. Adipose fin with long base, posterior end adnate to upper procurrent caudal-fin rays. Anal fin with ii,4,i (4) rays. Caudal fin weakly forked, with i,7,7,i (4) rays; lower lobe slightly longer than upper. Pelvic fin greatly enlarged, with convex distal margin and i,5 (4) rays; first ray greatly flattened and with numerous striae on ventral surface. Pectoral fin greatly enlarged, without spine and with i,8,i (1), i,9 (2) or i,l0 (1) rays; first ray greatly flattened and with numerous striae on ventral surface. Vertebrae 22+14=36 (2) or 23+14=37 (1).

Coloration. In 70% ethanol: brown on dorsal and lateral surfaces of the head and body, dark yellow on ventral region. Dorsal and caudal fins brown; dorsal surfaces of pectoral and pelvic fins brown, with light yellow ventral surfaces. Anal fin dark yellow. Dorsal surface of barbels brown, ventral surface dark yellow. Caudal fin with pale chevron-shaped band at base and broad, dark W-shaped band on most of middle.

In life ( Fig. 2 ): Olive brown on dorsal and lateral surfaces of head and body, fading to tan on ventral surfaces. Numerous pale spots densely distributed over dorsal surfaces of head and predorsal region. Dorsolateral surface of body with three indistinct tan-colored blotches: one below region between dorsal and adipose fins, second below adipose-fin origin, third below middle of adipose-fin base. Dorsal, pectoral and pelvic fins with dusky fin rays and hyaline fin membranes. Base of caudal fin with gently crescentic dark-brown bar; middle third of caudal fin with irregular, dark-brown w-shaped band. Dorsal surface of nasal and maxillary barbels olive brown, ventral surfaces tan. Mandibular barbels tan.

Distribution. This species is known from the Salween River drainage in Myanmar and western Thailand ( Fig. 3 ). It has been reported from the Sittang River drainage ( Thomson & Page, 2006), but this awaits confirmation.

Figures

FIGURE 1. Exostoma berdmorei, NIFI 1669, 66.4 mm SL; Thailand: Mae Jawang.

FIGURE 2. Exostoma berdmorei, live individual approx. 100 mm TL from Salween River drainage, Mae Hong Son Province, Thailand (specimen not preserved). Photograph by Nonn Panitvong.

FIGURE 3. Map showing collecting localities of Exostoma species in Thailand examined in this study. The type localities of E. effrenum and E. peregrinator are shown much further apart than they really are in order to easily distinguish between the two symbols.