Exostoma tibetana, Gong & Lin & Liu & Liu, 2018

Exostoma tibetana , new species

( Figs. 1–2 View FIGURE 1 View FIGURE 2 )

Exostoma labiatum: Wu et al. 1981: 78 View in CoL (Motuo County, Tibet, China); Wu & Wu 1991: 562–563 (Beibeng and Didong Village, Beibeng Town, Motuo County, Tibet, China)

Holotype. IHB 20161046 View Materials , 76.2 View Materials mm SL, China: Tibet Autonomous Region: Motuo County: Beibeng Town: Didong Village , a mountain stream flowing into the Yarlung Tsangpo River , 29°12’49” N, 95°15’26” E, 697 m above sea level; Pengcheng Lin et al., 31 October 2016. GoogleMaps

Paratypes. IHB 20161047–20161055 View Materials , 9 View Materials , 53.7 View Materials – 80.9 View Materials mm SL; same data as holotype GoogleMaps .

Diagnosis. Exostoma tibetana can be distinguished from all congeners by a combination of following characters: an adipose fin separate from the upper procurrent caudal-fin rays and incised at the posterior extremity of its base; the tip of pelvic-fin not reaching to the anus when adpressed; 10 branched pectoral-fin rays; and the following morphometric features: body depth at anus 10.4–12.3% SL, caudal-peduncle depth 6.7–8.6% SL and 33– 43% caudal-peduncle length, adipose-fin base 31.9–37.8% SL, snout length 48–58% HL, and eye diameter 8–10% HL.

Description. Morphometric data presented in Table 2. Head and body broad and greatly depressed. Dorsal profile rising gently from snout tip to dorsal-fin origin, sloping gently ventrally to end of caudal peduncle. Ventral profile flat from snout to anal-fin base; sloping gently dorsally to end of caudal peduncle. Body depth at anus 10.4– 12.3% SL; caudal-peduncle depth 6.7–8.6% SL and 33–43% caudal-peduncle length. Head medium size. Snout blunt and depressed, length 48–58% HL. Rostral cap with groove in anterior edge of mouth; with papillae on surface. Nares situated almost midway between snout tip and anterior orbital margin. Eye small, rounded, subcutaneous; located dorsally in posterior half of head; diameter 8–10% HL. Barbels in four pairs. Maxillary barbels flattened, with surrounding flap of skin and rounded tip; extending beyond pectoral-fin origin and gill opening. Nasal barbels with small flap of thin skin fringing posterior margin, just reaching to anterior orbital margin. Inner mandibular barbels short and slightly flattened, originating from notch on posterior margin of lower lip; tip not reaching to vertical line through pectoral-fin origin. Outer mandibular barbels slightly flattened, situated lateral to inner mandibular barbel; reaching to anterior base of pectoral fin.

Mouth inferior; opening transversely. Lips thick, fleshy, and papillate; anterolateral surfaces covered with anastomosing, rounded plaques. Post-labial fold continuous. Lower lip with prominent labial fold bearing entire posterior margin; notched at insertions of inner mandibular barbels and middle of fold. Upper and lower jaw each divided medially by fleshy medial frenum. Jaw teeth distally flattened and oar-shaped. Upper jaw tooth in two rounded triangular patches narrowly separated at midline on upper jaw; lower jaw teeth situated in two wellseparated and roughly triangular patches.

Dorsal fin with i,6 rays; origin anterior to pelvic-fin origin; fin margin slightly concave. Adipose fin long and deep; posterior margin separated from upper procurrent caudal-fin base and incised at the posterior extremity of its base; adipose-fin base length 31.9–37.8% SL. Pectoral fin large, with i,10 rays; margin broadly rounded; first unbranched ray broad with regular striae on ventral surface. Pelvic fin enlarged, with i,5 rays; margin gently concave; first unbranched ray broad with regular striae on ventral surface; tip of fin not reaching to the anus when adpressed. Anal fin with i,4 (2) or i,5 (8*) rays; posterior margin slightly concave; tip of fin almost reaching midway between its origin and caudal-fin base. Caudal fin lunate; tips of lobes pointed. Skin of body smooth and naked. Lateral line complete and mid-lateral.

Coloration. In 75% ethanol: dorsal and lateral surfaces of body yellow-brown; ventral region of body anterior to anal-fin origin light yellow or grey-white, with grayish spots on margin. Dorsal, pectoral, pelvic, anal and caudal fins yellow-brown with hyaline interradial membranes, ventral surfaces of pectoral and pelvic fin white or yellow. Adipose fin yellow-brown, with hyaline margin.

Distribution. This species is known from the lower Yarlung Tsangpo River drainage in Motuo reach, southeastern Tibet, China. ( Figs. 3–4 View FIGURE 3 View FIGURE 4 ) Etymology. The specific epithet was derived from its type locality: Tibet. An adjective.