Exostoma tibetana, a new glyptosternine catfish from the lower Yarlung Tsangpo River drainage in southeastern Tibet, China (Siluriformes: Sisoridae) Author Gong, Zheng Author Lin, Pengcheng Author Liu, Fei Author Liu, Huanzhang text Zootaxa 2018 2018-12-06 4527 3 392 402 journal article 27843 10.11646/zootaxa.4527.3.8 040488e3-5906-4e86-8722-532417da4652 1175-5326 2612357 B0D4923F-F02E-4AB8-9B7E-68ADEB66E1EC Exostoma tibetana , new species ( Figs. 1–2 ) Exostoma labiatum : Wu et al. 1981 : 78 (Motuo County, Tibet , China ); Wu & Wu 1991: 562–563 (Beibeng and Didong Village, Beibeng Town, Motuo County, Tibet , China ) Holotype . IHB 20161046 , 76.2 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 . Paratypes . IHB 20161047–20161055 , 9 , 53.7 – 80.9 mm SL; same data as holotype . FIGURE 1. Exotoma tibetana , holotype, IHB 20161046, 76.2 mm SL; China: Tibet: a mountain stream of the lower Yarlung Tsangpo River. FIGURE 2. Exotoma tibetana , holotype, IHB 20161046, 76.2 mm SL; China: Tibet: a mountain stream of the lower Yarlung Tsangpo River; dorsal and ventral views of head. 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. TABLE 2. Morphometric data of Exostoma tibetana (holotype IHB 20161046; paratypes: IHB 20161047–20161055, n=9). SD = standard deviation.

Holotype	Holotype and paratypes
Range	Mean	SD
Standard length (SL, mm)	76.2	53.7–80.9	73.1	8.3
In percent of SL
Body depth at anus	11.8	10.4–12.3	11.3	0.6
Body depth at dorsal-fin origin	13.6	11.5–13.7	12.7	0.7
Body width at dorsal-fin origin	16.4	14.0–16.7	15.4	1.1
Head length	21.3	19.0–22.5	20.9	1.1
Head depth	9.8	9.4–11.2	10.4	0.6
Head width	20.7	18.4–21.2	19.7	0.9
Dorsal-fin base length	9.2	8.8–10.8	9.7	0.7
Adipose-fin base length	34.6	31.9–37.8	34.6	1.9
Pectoral-fin length	24.4	22.2–25.0	23.1	1.0
Pelvic-fin length	18.8	16.8–19.8	18.4	0.8
Anal-fin base length	5.4	4.9–5.7	5.4	0.2
Predorsal length	39.2	36.0–39.3	38.4	1.0
Prepectoral length	14.3	14.3–17.9	16.0	1.0
Prepelvic length	45.9	43.7–48.1	45.9	1.4
Preanal length	76.0	73.0–77.5	75.4	1.3
Caudal-peduncle length	19.8	18.6–20.6	19.7	0.5
Caudal-peduncle depth	7.3	6.7–8.6	7.5	0.6
In percent of HL
Snout length	56	48–58	55	3.3
Head depth	46	46–54	50	2.4
Head width	98	87–102	94	4.9
Eye diameter	8	8–10	9	0.7
Interorbital space	33	27–35	32	2.9
Maxillary barbel length	78	69–88	79	5.5
Nasal barbel length	36	31–40	35	2.8
Inner mandibular barbel length	11	9–11	10	0.8
Outer mandibular barbel length	23	20–29	24	2.7
In percent of caudal-peduncle length
Caudal-peduncle depth	37	33–43	38	3.1

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