Homatula nigra, Li & Che & Zhou, 2019

Li, Xu, Che, Xing-Jin & Zhou, Wei, 2019, Loaches of Homatula (Teleostei: Nemacheilidae) from the upper Salween River in Yunnan, China with description of three new species, Zootaxa 4711 (2), pp. 330-348 : 341-342

Homatula nigra sp. nov.

( Fig. 2C , Fig. 10 )

Holotype. SWFC 1901005, 99.8 mm SL; China: Yunnan: Baoshan City: Changning County: Gengga Town : Xiangshui Village (24°29’7.26”N 99°29’39.94”E); collected by XJ. Che , 8 Jan. 2019.

Paratypes. SWFC 1901001-1901004, 4 ex., 92.0– 109.1 mm SL; other data same as the holotype . SWFC 0411005-0411009, 5 ex., 55.2–87.4 mm SL; collected by X. Li & W. Zhou, 23 Nov. 2004; other data same as the holotype .

Diagnosis. Homatula nigra differs from other species of the densely-scaled group in Homatula by the following combination of characters: no marks on flank in H. nigra (vs. vertical bars on flank along lateral line in all congeners of densely-scaled group in Homatula ); no free protrusions between pelvic fins (vs. pair of free protrusions between pelvic fins in H. pycnolepis ); gill opening smaller, its upper angle level with lower edge of eye (vs. gill opening larger, its upper angle aligned with middle point of eye in H. acuticephala , H. anguillioides , H. coccinocola , H. erhaiensis , and H. pycnolepis ) ( Fig. 5 ); with pelvic axillary lobe (vs. without pelvic axillary lobe in H. acuticephala and H. anguillioides ); marked notch on lower jaw (vs. lower jaw spoon-shaped and lacking notch in H. erhaiensis and H. wuliangensis ); dorsal-fin base shorter than longest branched dorsal-fin ray (vs. dorsal-fin base longer than longest branched dorsal-fin ray in H. acuticephala , H. anguillioides , H. cryptoclathrata , H. erhaiensis , and H. wuliangensis ) ( Tables 1 & 2 ).

Description. Based on holotype and 9 paratypes, maximum standard length is 109.1 mm. Morphometric data are shown in Table 2 . Dorsal-fin rays iii, 8½; anal-fin rays iii, 5½; pectoral-fin rays i, 9–10; pelvic-fin rays i, 7; caudal-fin branched rays 9+8; vertebrae 4+41 (2 specimens)–42 (1 specimen).

Body elongate and cylindrical, anteriorly slightly depressed, posteriorly compressed laterally. Maximum body depth immediately in front of dorsal fin. Dorsal and ventral profiles almost straight. Except for scaleless head and thorax, body is entirely covered by small scales, with scattered scales on abdomen. Caudal peduncle compressed laterally. Lateral line complete, extending directly along midline of body.

Head short and depressed in frontal view, wider than high, roughly triangular in dorsal view. Snout blunt, slightly shorter than postorbital length of head. Eye small, close to dorsal profile of head, invisible from ventral view. Interorbital space wide and flat. Nostrils closely set, nearer to anterior margin of eye than to snout tip; anterior nare pierced in front side of a flap-like tube with pointed tip.

Mouth inferior and arched. Lips thick, slightly furrowed, but not papillated; upper lip with small median incision, lower lip with marked median incision. Jaws covered by lips; upper jaw with well developed processus dentiformis corresponding with marked notch on lower jaw. Three pairs of barbels; two rostral pairs, inner barbel not reaching corner of mouth and outer barbel pair reaching vertical line of anterior nostril; one maxillary barbel pair long, reaching to vertical line between middle and posterior margin of eye ( Fig. 7C ).

Dorsal fin with 3 simple and 8–9 branched rays; distal margin convex; origin slightly forward of midway between snout tip and caudal-fin base. Pectoral fin with 1 simple and 9–10 branched rays, inserted slightly posterior to vertical through posteriormost point of operculum, tip of longest fin ray not extending beyond halfway to insertion of pelvic fin. Pelvic fin with 1 simple and 6–7 branched rays, inserted below first or second branched rays of dorsal fin, tip of longest fin ray not extending beyond half distance between pelvic-fin insertion and anal-fin origin. Pelvic axillary lobe with pointed tip. Anal fin with 3 simple and 5 branched rays, with convex distal edge; origin closer to pelvic-fin insertion than to caudal-fin base. Posterior margin of caudal fin oblique or micro-concave. Caudal peduncle uniformly deep; with adipose crests along dorsal and ventral midlines. Adipose crest along dorsal midline of caudal peduncle not extending through posterior end of anal-fin base. Anus located posteriorly, approximately 1/3 the distance between the pelvic-fin insertion and anal-fin origin, closer to the caudal-fin base.

Coloration: Flank of fresh specimen black with no bars, dorsum of body dark brown, abdomen pale yellow. After fixation in 95% alcohol, flank is brown, abdomen grayish yellow. Dark brown vertical bar on caudal-fin base. Dorsal surface of pectoral, pelvic, and anal fins reddish orange; dorsal and caudal fins yellowish ( Fig. 10D ).

Distribution: Known only from Damengtong-he, a branch of the Mengboluo-he, the first tributary of the Nujiang drainage (the upper Salween River) ( Fig. 8 ).

Habitat and Ecology: Homatula nigra is omnivorous, mainly feeding on algae attached to rocks, organic residues, and small aquatic insects. It inhabits flowing and clear stream environments, dwelling at the bottom and shuttling back and forth among rocks and gravel.

Etymology: The specific epithet, nigra , an adjective, is from the Latin word niger (black), alluding to the pattern of bars on the flank in front of the dorsal-fin origin.

Remark: The body color of H. nigra is unique compared with the body color of other species of Homatula . There are no bars on its flank and the whole body is black. However, when the specimens are fixed and preserved in alcohol, the discoloration of the specimen is significant and "irregular cloud marks" will appear on the flank. The flank of the fresh specimen collected in Jan. 2019 was black with no bars, the dorsum of the body was dark brown, and the abdomen was pale yellow ( Fig. 10D ). In the field, we noticed that when individuals of fresh specimens of Homatula are pushed and squeezed in a narrow vessel, the color on the body will be lost soon after touching, even before fixing in alcohol; furthermore, the discoloration is uneven when the specimen is fixed with alcohol causing the fixed samples to show a false appearance of the "irregular cloud marks." This phenomenon is also common in fresh specimens of the families Balitoridae and Nemacheilidae .

Figures

FIGURE 2. Relationship between anterior end of adipose crest and anal-fin base of Homatula. (A) H. anteridorsalis, SWFC 1610019, paratype, 108.1 mm SL; (B) H. cryptoclathrata, SWFC 1002001, holotype, 138.1 mm SL; (C) H. nigra, SWFC 1901005, holotype, 99.8 mm SL; (D) H. pycnolepis, SWFC 0612085, 99.6 mm SL; (E) H. laxiclathra, SWFC 1810010, 97.0 mm SL); (F) H. nanpanjiangensis, SWFC 1903001, 97.1 mm SL.

FIGURE 5. Gill openings of Homatula. (A) Larger gill opening; upper angle aligned with middle point of eye (H. pycnolepis, SWFC 0612085, 99.6 mm SL); (B) smaller gill opening; upper angle level with lower edge of eye (H. cryptoclathrata, SWFC 1610006, holotype, 121.6 mm SL).

FIGURE 7. Mouths of Homatula. (A) H. anteridorsalis, SWFC 1610006, holotype, 121.6 mm SL; (B) H. cryptoclathrata, SWFC 1002001, holotype, 138.1 mm SL; (C) H. nigra, SWFC 1901005, holotype, 99.8 mm SL; (D) H. pycnolepis, SWFC 0612085, 99.6 mm SL.

FIGURE 8. Distribution map of the densely-scaled group of Homatula. A symbol may represent several adjacent localities.

FIGURE 10. Homatula nigra, (A–B, D) SWFC 1901005, holotype, 99.8 mm SL; (C) SWFC 0411007, paratype, 87.4 mm SL, China: Yunnan: Baoshan City: Changning County: Gengga Town: Xiangshui Village.