Physoschistura dikrongensis, Lokeshwor & Vishwanath, 2012

Lokeshwor, Y. & Vishwanath, W., 2012, Physoschistura dikrongensis, a new loach from Arunachal Pradesh, India (Teleostei: Nemacheilidae), Zootaxa 3586, pp. 249-254 : 250-253

Physoschistura dikrongensis sp. nov.

( Fig. 1)

Type material. Holotype. MUMF 11091 /3, 44.6 mm SL, male; India: Arunachal Pradesh: from Dikarong river at Doimukh (Brahmaputra basin); 27°08'19"N, 93°44'51"E, 120 m above sea level, K. Nebeshwar et al., 8 April 2007.

Paratopotypes. MUMF 11090 /2, 2 specimens, 40.1–46.8 mm SL, females . MUMF 11091 /4, 4 specimens, 41.4–51.7 mm SL, males. ZSI FF 423, 2 specimens, 41.0 mm SL, male; 41.5 mm SL, female .

Diagnosis. A Physoschistura distinguished from its congeners in having the following combination of characters: two V-shaped dark brown bars across caudal fin; 11–15 irregular dark brown bars on body; dorsolateral and dorsal portion of head mottled dark brown; incomplete lateral line with 70–85 pores; 4 simple and 8½ branched dorsal-fin rays; 4 simple anal-fin rays; caudal fin with 8+7 branched rays; large axillary pelvic-fin lobe; suborbital flap in male; 9 pores in preoperculo-mandibular canal.

Description. Morphometric data are given in Table 1. Body moderately elongate and stout. Dorsal profile elevating evenly from tip of snout to origin of dorsal fin, then slanting gently ventrally to the vertical level of analfin origin, continuing horizontally to caudal base. Anterior portion of body cylindrical in cross section, posterior portion compressed laterally from anal-fin base to caudal-fin base. Ventral profile almost flat from tip of snout to caudal base. Head slightly depressed, almost as broad as high at eye and supraoccipital region. Snout rounded.

Dorsal fin with 4 simple and 8½ branched rays, articulated in advance of pelvic fin. Distal margin of dorsal fin slightly convex. Anal fin with 4 simple and 5½ branched rays, its distal margin reaching two-thirds distance from anal-fin origin to caudal peduncle. Pectoral fin with 1 simple and 9 branched rays, reaching two-thirds distance to pelvic-fin base. Pelvic fin with 1 simple and 7 branched rays, origin at vertical from 2nd or 3rd branched dorsal-fin rays. Distal margin of pelvic fin not reaching vent when adpressed, leaving a distance of half eye diameter. Axillary pelvic-fin lobe large. Caudal fin with 8 upper and 7 lower branched rays, forked, lobes equal in length. Caudal peduncle 1.2–1.4 times longer than deep, with low dorsal and ventral adipose crests on posterior half. Largest recorded size: 51.7 mm SL male (MUMF 11091/4).

Body covered by partly overlapping embedded minute scales. No scales present on ventral surface anterior to pelvic fin origin. Lateral line incomplete, reaching vertical to anal-fin origin and straight with 70–85 pores. Cephalic lateralis system with 9 supraorbital, 3+9 infraorbital, 9 preoperculo-mandibular and 3 supratemporal pores. Unculi present on lips, barbels, and pectoral fin rays.

Anterior nostril pierced on anterior side of a low flaplike pointed tube. Mouth arched, 1.6–1.8 times wider than long. Upper lip finely and regularly pleated with a median incision. Lower lip with a median interruption, forming two lateral broadly triangular pads with a wide median furrow between them ( Fig. 2). Processus dentiformis prominent. No median notch on lower jaw. Inner rostral barbel reaching to maxillary barbel; outer barbel reaching vertically to posterior orbital rim. Maxillary barbel extends slightly beyond posterior orbital rim. Free posterior chamber of air bladder well formed, spherical, and not encapsulated. Intestine with a bend, a bit distant behind the stomach and forming a loop ( Fig. 3).

Sexual dimorphism. Male with prominent spoon-shaped suborbital flap (Fig. 4).

Color. In 10% formalin: yellowish cream background with 11–15 irregular dark brown bars on body. Color is darker on dorsal surface and lighter on ventral surface. Bars are variable in shape, complete on back or with 3–4 small saddles between them. Predorsal bars numerous, small, and appear as split large bars. Bars behind dorsal fin meet or nearly so on ventral surface, while those anterior to dorsal-fin origin end at level of pectoral-fin insertion. Anteriormost bar may be fragmented dorsolaterally. Bars become fainter and narrower towards venter. Interspace between bars thinner than bars. Caudal-peduncle bars usually interrupted into small saddles on dorsal midline and appear as blotches midlaterally. Dorsal and dorsolateral portions of head mottled with dark brown spots, which become fainter towards ventral surface. Conspicuous black spot at dorsal-fin origin. Dorsal fin with three bands, rest of fin hyaline. Caudal-fin base with irregular black bar extending from dorsal to ventral midlines. Caudal fin hyaline with two V-shaped bars pointing anteriorly; first bar at first branching point of rays and second bar midway between first bar and posterior margin of branched rays; rest of fin hyaline. Entire length of first branched pectoralfin ray dusky.

Distribution. India: Arunachal Pradesh: Dikrong River at Doimukh, Brahmaputra basin ( Fig. 5).

Etymology. The species is named after its type locality, Dikrong River.