Holotype: YNU2011082201, 75.98 mm SL; China: Yunnan Province, Yingjiang County, Nabang Township, downstream of the River Mengnai (a tributary of the upper Irrawaddy), 24°42′54.54″ N, 97°34′06.44″ E, 247 m, 22 August 2011, Ziming Chen.

Paratype: YNU2011082202, 61.01 mm SL; China: Yunnan Province, Yingjiang County, Nabang Township, downstream of the River Mengnai (a tributary of the upper Irrawaddy), 24°42′54.54″ N, 97°34′06.44″ E, 247 m, 22 August 2011, Ziming Chen.

Diagnosis: A. yunnanensis is distinguished from congeners in having the following combination of characters: skin smooth with complete lateral line, laterosensory pores haphazardly distributed in pairs; mouth sub-terminal with upper jaw slightly longer than the lower one; lips with papillae, adipose-fin short, with a low and smooth outer edge, posterior end of which rounded and separated from dorsal procurrent rays of caudal-fin by a remarkable notch; no pinnate like rays on caudal-fin rays; body depth at anus 14.1–14.6 % SL; head length 19.9–20.4 % SL; head depth 9.9–10.1 % SL; eye to nasal barbel 9.3– 10.2 % SL; caudal peduncle length 19.6–19.9 % SL; caudal peduncle depth 13.5–13.6 % SL.

There were five species of Amblyceps with caudal-fins truncate and emarginate, namely, A. yunnansis, A. apangi, A. murraystuarti, A. torrentis (caudal-fin emarginated according to Linthoingambi & Vishwanath 2008) and A. cerinum with a truncate caudal-fin (vs. deeply forked and emarginated). Compared with those species, a shorter adipose-fin base (19.6–21.5 % SL) and a unique tooth band can set A. yunnansis apart immediately. It further differs from A. apangi in having a more slender caudal peduncle (caudal peduncle depth 13.5–13.6 % SL vs. 15.0–16.8 % SL); a shorter space between the eye and nasal barbel (eye to nasal barbel 9.3–10.2 % HL vs. 13.0– 16.0 % HL); a less developed rictal fold (vs. large and very well developed); teeth in upper jaw with no gap (vs. with a narrow gap), from A. murraystuarti in having upper jaw slightly longer than the lower (vs. lower longer); a distinct boundary between adipose fin and caudal procurrent rays; a longer pelvic-fin length (11.2–11.6 % SL vs. 7.4–8.8 % SL); a longer caudal-fin (length 18.1 % SL vs. 13.7–16.6 % SL), from A. torrentis in having a sub-terminal jaws (vs. equal jaws); no separation in the premaxillary teeth (vs. a narrow gap); a slightly compressed body (body depth 14.1–14.6 % SL vs. 15.3–17.3 % SL); a greater head length (19.9–20.4 % SL vs. 16.8–18.9 % SL); a shorter interorbital space (24.0–24.5 % HL vs. 29.0– 37.0 % HL); a longer predorsal length (24.3–24.9 % SL vs. 20.6–22.7 % SL); a shorter caudal peduncle (caudal peduncle length 19.6–19.9 % SL vs. 21.0–24.3 % SL), from A. cerinum in having skin smooth (vs. in small granular papillae) and lateral line completed (vs. incomplete); a less depressed head (head depth 9.9–10.1 % SL vs. 7.0–9.2 % SL); a less slender tail (caudal peduncle length 19.6–19.9 % SL vs. 21.9–24.5 % SL; caudal peduncle depth 13.5–13.6 % SL vs. 9.2– 11.2 % SL).

Description: Morphometric data shown in Table 1. Body elongate, covered with thick semitransparent mucus, anterior region of pelvic-fin subcylindrical, posterior region of pelvic-fin compressed gradually. Skin smooth with uniform colouration, lateral line midlateral and complete. Remarkable cup-like skin flap above the origin of the pectoral-fin, posterior to the gill-openings. Dorsal profile from lateral view, cephalic area gently convex; dorsal-fin region straight; postdorsal part from end of dorsal-fin base to end of adipose-fin base convex. Ventral profile concave from pectoral-fin to caudal-fin base; preanal area of ventral profile presenting two convexs: one from the tip of snout to the start of pelvic-fin, and the other from end of pelvic-fin to the anal-fin origin. Anus and urogenital openings located very close to depressed pelvic-fin (distance of anus to posterior margin of pelvic-fin 5.3– 7.5 % of the distance to anal-fin origin) (Fig. 2).

Head depressed with cheek muscles being a little swollen residing at each side of the middle groove on the roof of head. Eyes subcutaneous, small and subovoid (eye diameter 13.4–15.2 % HL). Nostrils close together, separated by a nasal barbel, the anterior naris being a complete tube-like membrane, while posterior naris being an incomplete tube whose anterior edge basally connects to nasal barbel; posterior rim of posterior narial membrane with notch. Gill openings broad, gill membranes united to each other, but free from isthmus, with 10 branchiostegal rays in each side. Oblate barbels in four pairs, extending from each side of jaws. Maxillary barbel longest, originating from end of upper and lower rictal fold of lips, extending to posterior margin of pectoral-fin base; nasal barbel extending almost to opercle; outer mandibular barbel extending to middle of pectoral-fin base; inner mandibular barbel offset from midventral line into two and outer mandibular barbel, extending to middle of pectoral-fin base.

Mouth sub-terminal, with upper jaw a little longer than the lower one, anterior rim of lower jaw not visible dorsally. Lips fleshy and slightly fimbriated, the less developed rictal fold extending to the bases of maxillary barbel on both sides; oral teeth small and villiform, premaxillary teeth in a single broad band, with a very shallow incision in the middle of the posterior edge, but no separation gap in the midline, dentary teeth in one narrow crescent band with a very narrow gap in the midline (Fig. 3).

Fins wrapped in thin skin, base of which somewhat swollen; dorsal-fin originating vertically at the middle length of pectoral-fin, with one very weak spine wrapped in very thin skin and four rays. Adiposefin base short, in the form of low and smooth edge, originating approximately at vertical point of anterior one quarter of the length of the anal-fin base, the boundary to the caudal-fin presented by a distinct groove (Fig. 1). Anal-fin with a straight anterior margin and convex posterior rim, with 10 rays; pectoral-fin without spine, posterior margin convex, extending nearly to the level of middle of dorsal-fin, with seven rays. Pelvic-fin depressed, tip of which far for reaching the anal-fin origin, with rays seven; caudal-fin truncated without pinnate rays, dorsal procurrent rays of which extending quite anterior to its base.

Colour in living specimens: In fresh specimens: body brownish grey, dorsal and flank region of anterior 2/3 of body gray white, shade into light brown grey posterior. Area of swollen cheek muscles on dorsal surface of the head light brown, abdominal region white anteriorly and orange posteriorly. Fins with margins whitish to light yellow, dorsal-fin dark grey; anal-fin slate grey; pelvic and pectoral-fins covered by translucent light yellow membrane; adipose-fin light brown; middle of caudal-fin dark grey, and fading dorsally and ventrally. Nasal and maxillary barbels light grey to yellow. Mandibulary barbel light yellow with lighter abaxial margin.

Colour in formalin: Presence of a darker colouration, shown by grey dorsal surfaces, grey-brown profiles and yellow ventral regions. Light yellow orange laterally.

Distribution and habitat: Currently only from the River Mengnai (24°42′54.54″ N, 97°34′06.44″ E, 247 m), which is located near Nabang Township, Yingjiang County, in the west of Yunnan Province, China (Fig. 4). A. yunnanensis was found hiding under boulders in groups in shallow rapids of hill streams. The River Mengnai is a fast-flowing hill streams which twists its way through dense forest. The river bed has large boulders, cobbles, gravel, and sand. The wet rocks are covered with many diatoms (Fig. 5). Water temperature was 22.8 °C (at 12:40 p.m., 22 August 2011), water pH 7.0, and transparency 45 cm. Etymology: From Yunnan Province and the latin suffix “ensis”, meaning from a place.