Mustura daral, Rameshori & Chinglemba & Darshan & Vishwanath, 2022

Rameshori, Yumnam, Chinglemba, Yengkhom, Darshan, Achom & Vishwanath, Waikhom, 2022, Mustura daral, a new species of stone loach from Arunachal Pradesh, Northeast India (Teleostei: Nemacheilidae), Zootaxa 5129 (2), pp. 285-294 : 286-291

Mustura daral , new species

( Fig. 1–2 )

Holotype. MUMF18061 , male, 59.6 mm SL; India: Arunachal Pradesh: East Siang District: Siang River (Brahmaputra drainage), at Pasighat , 28°01’57”N, 95°22’05”E, Elevation 144 m asl; Achom Darshan & party, 21 February 2015.

Paratypes. MUMF 18062–18074 , 13 , males, 56.7–66.8 mm SL ; MUMF 18075 – MUMF 18078 , 4 , females, 64.1–70.4 mm SL; same data as holotype .

Diagnosis. Mustura daral is distinguished from its congeners in the Brahmaputra drainage by having darkbrown saddles on the dorsum descending onto the flank forming 9–10 regularly set and shaped dark-brown bars (vs. 11–15 irregular set and shaped bars on the flank in M. dikrongensis , 14–23 in M. subhashi , and 11–18 in M. walongensis , 9–10 vertically elongated blotches on the flank alternating with saddles in M. harkishorei ). The new species is further distinguished from M. dikrongensis by having 10–11 branched pectoral-fin rays (vs. 9), a plain head (vs. mottled with dark-brown spots), dorsal fin with one (vs. three) row of black spots, the bar at caudal-fin base dissociated into two black blotches (vs. complete), 9+8 (vs. 8+7) branched caudal-fin rays, pelvic-fin length 17.2– 20.6% SL (vs. 14.9–17.1), and caudal-peduncle length 10.5–14.0% SL (vs. 14.5–16.6). It is further distinguished from M. subhashi by having regular set and shaped pre-dorsal bars (vs. saddles descending onto the flank split into numerous thin, irregular set and shaped bars or fused altogether with adjacent bars in some individuals), processus dentiformis conspicuous (vs. feeble), mouth about 1.7–2.3 (vs. 1.2–1.3) times wider than long, body depth at the dorsal-fin origin 14.2–16.6% SL (vs. 18.0–21.2), and caudal-peduncle depth 9.7–11.0% SL (vs. 12.0–13.8). The new species is further distinguished from M. walongensis by having a complete (vs. incomplete) lateral line, a plain head (vs. mottled with dark-brown spots), the bar at caudal-fin base dissociated into two black blotches (vs. complete, W-shaped), two rows of V-shaped black spots on the caudal fin (vs. absence), outer rostral barbel reaching vertical of posterior margin of posterior nostril (vs. almost reaching vertical of posterior orbital margin). It is further distinguished from M. harkishorei by lacking a filamentous extension of the second branched pectoral-fin ray (vs. having), having lower caudal-fin lobe slightly longer than upper one (vs. equal), 9+8 (vs. 7+8) branched caudal-fin rays, and caudal-peduncle depth 9.7–11.0% SL (vs. 6.8–8.7). M. daral is distinguished from M. tuivaiensis from the geographically adjacent Barak drainage by having saddles descending onto the flank forming 9–10 regular set and shaped dark-brown bars (vs. 12–14 irregular set and shaped, vertically elongated blotches alternating with saddles), 10–11 branched pectoral-fin rays (vs. 9), a black spot at base of unbranched dorsal-fin rays (vs. absence), 9+8 (vs. 8+7) branched caudal-fin rays, and intestine with a loop (vs. bend) behind stomach.

Description. General appearance as in Fig. 1–2 . Morphometric data of holotype and 17 paratypes are given in Table 1 . Body moderately elongate, cross-section sub-cylindrical anteriorly, and compressed posteriorly. Dorsal profile arched, elevating gently from tip of snout to nape, then evenly to dorsal-fin origin, sloping gently to caudalfin base. Behind dorsal fin, body depth decreasing slowly to caudal-fin base. Ventral profile of body slightly arched but more or less straight up to anal-fin origin, then inclined evenly towards caudal-fin base. Head slightly depressed, maximum head width 2.1–2.8 times interorbital width. Eye spherical, not visible in ventral view. Snout rounded in dorsal view, blunt in lateral view. Caudal peduncle 1.0–1.4 times longer than deep, with low dorsal and ventral adipose crests on posterior half. Largest recorded size 70.4 mm SL (MUMF 18075).

Dorsal fin with 4 (18) simple and 8½* (17) or 9½ (1) branched rays, origin slightly in advance of pelvic-fin origin; distal margin convex. Anal fin with 3 (18) simple and 5½ (18) branched rays, not reaching caudal-fin base when adpressed, separated by about a gap equal to eye diameter. Pectoral fin with 1 (18) simple and 10* (16) or 11 (2) branched rays, reaching about a little more than two-thirds of distance to pelvic-fin origin. Pelvic fin with 1 (18) simple and 7 (18) branched rays, origin below base of branched dorsal-fin ray 1 or 2; distal margin reaching beyond half the distance to anal-fin origin, not reaching to anus when adpressed. Axillary pelvic-fin lobe present, entirely free and prominent. Anus situated about an eye diameter in front of anal fin. Caudal-fin with 9+8 (18) branched rays, forked, lower lobe slightly longer than upper one.

Body completely covered with deeply embedded minute scales except on chest and belly in front of anal-fin origin. Lateral line complete, with 78–86 pores. Cephalic lateral line system with 8 supraorbital, 3+9 infraorbital, 8–9 preoperculo-mandibular and 3 supratemporal pores. Unculi present on lips and barbels.

Anterior nostril pierced at front of low pointed flap-like tube. Posterior and anterior nostrils adjacent. Mouth strongly arched, about 1.7–2.3 times wider than long ( Fig. 3a ). Lips thin, fleshy. Upper lip finely and regularly pleated with a small median notch. Processus dentiformis present, no corresponding median notch on lower jaw. Lower lip with a wide median interruption, not in contact medially; two halves oriented in an acute angle forming triangular cushions, partly free from jaw and connected to isthmus by a frenum; and with few shallow wrinkles on either side. Tip of lower jaw exposed. Inner rostral barbel reaching corner of mouth; outer rostral barbel reaching vertical of posterior margin of posterior nostril; maxillary barbel reaching vertical of posterior margin of eye. Two halves of air bladder capsule very widely separated and connected by a manubrium ( Fig. 3b ). Free posterior chamber of air bladder absent. Intestine with loop, behind posterior part of stomach ( Fig. 3c ). Vertebrae: 21 + 13 = 34 (2).

Sexual dimorphism. Male with a distally rounded, prominent suborbital flap, with small tubercles present along its posterior extremity ( Fig. 3d ); a rigid pectoral fin, slightly curled upwards. Branched pectoral-fin ray 1 about three times wider than following rays, slightly falcate, branched only once, without membrane between ossified elements except near tip. Branched pectoral-fin ray 2 longest, branched once. Following branched pectoralfin ray branched twice, last branched ray branched once; membrane present between branches. Thick unculiferous pads present on dorsal surface of pectoral-fin rays; dorsally branched ray 1 covered by densely-set small conical tubercles along its posterior flange ( Fig. 3e ); also tubercles present on posterior flanges of branched rays 2 to last, more in number and prominent on branched rays 2–4 than following rays, number of tubercles on posterior flanges decreases from branched rays 4 to last towards pectoral-fin base.

Female without suborbital flap, slit or groove. In female, branched pectoral-fin ray 1 slightly wider than adjacent rays, with moderately thick unculiferous pads and without tubercles ( Fig. 3f ); branched once near middle of ray, not near tip; membranes present between branches. Branched pectoral-fin ray 3 longest.

Coloration. In 10% formalin, body with 9–10 dark-brown saddles on dorsum (3–4 saddles in pre-dorsal, 3 in sub-dorsal and 3 in post-dorsal region), all continuous with regular set and shaped dark-brown bars on flank. Bars on caudal peduncle meeting their antimere ventrally to form a complete ring. Bars wider than interspaces, interspaces of posterior bars wider than between anterior bars. Background colour beige on dorsum and dorsolaterally; beige to dull white ventrally. Head dark-brown dorsally, beige to dull white laterally and ventrally. All three pairs of barbels dull white. A small black blotch at upper and a black, vertically elongated blotch at lower caudal-fin base.

Dorsal fin hyaline, with a black spot at base of simple and branched rays 1–2, one row of black spots at about mid-length of dorsal-fin. Pectoral-, pelvic- and anal-fin proximal portion beige; distal portion hyaline. Caudal fin with 2 rows of V-shaped black spots, with vertices pointed towards caudal-fin base, one at mid-length, another near the posterior margin of caudal-fin.

Distribution and habitat. Presently known from the Siang River at Pasighat (Brahmaputra drainage), Arunachal Pradesh, Northeast India ( Fig. 4 ). The new species was collected from medium to fast flowing water over a substrate of sand, cobbles and pebbles ( Fig. 5 ).

Etymology. The specific epithet is derived from the local name of the fish in Adi Tribe: ‘Daral’. A noun.

Remarks. A key to species of the genus Mustura of the Eastern Himalayan region is presented below. Mustura daral is here compared with its congeners occurring in different drainages of South and Southeast Asia, viz., the Chindwin-Irrawaddy, Kaladan, Mekong, Chao Phraya, and Salween drainages. The new species differs from its members of the genus in the Chindwin-Irrawaddy drainage by its regularly set and shaped saddles on the back, saddles descends on the flank forming 9–10 regularly set and shaped bars (vs. 6–10 very irregularly set and shaped blotches or bars alternately arranged with irregular shaped saddles in M. celata , 13–17 in M. chindwinensis , 12– 13 in M. taretensis , 9–12 vertically elongated blotches in M. prashadi , 6–9 short regularly set and shaped bars descending slightly below lateral line in M. shuensis , 12–14 irregular set and shaped bars in M. tigrina , 18–20 in M. yunnaniloides ). M. daral is further distinguished from M. celata by presence (vs. absence) of a small median notch in the upper lip, pelvic fin not reaching (vs. reaching) the anus, and outer rostral barbel reaching vertical of posterior margin of posterior nostril (vs. reaching vertical of middle of eye). The new species is further distinguished from M. chindwinensis by having more pectoral-fin rays (i+10–11 vs. i+9), more branched upper caudal-fin rays (9+8 vs. 8+8), a plain head (vs. with dark-brown blotches), and rows of spots on the dorsal and caudal fins (vs. absence). It is further distinguished from M. prashadi by having mouth 1.7–2.3 (vs. 1.4–1.5) times wider than long, body depth at the dorsal-fin origin 14.2–16.6% SL (vs. 18.4–23.3), and a smaller eye (eye diameter 14–20% DHL vs. 24.0–29.1). The new species is further distinguished from M. shuensis by having the lower jaw without (vs. with) a median notch, the female without (vs. with) a suborbital slit, the distal margin of dorsal fin convex (vs. slightly concave), body depth at the dorsal-fin origin 14.2–16.6% SL (vs. 17.5–23.0), and caudal peduncle 1.0–1.4 (vs. 0.8–1.0) times longer than deep. M. daral is further distinguished from M. taretensis by having a plain nape (vs. rhomboid shaped dark-brown mark on the nape), pelvic fin not reaching (vs. reaching) the anus, and mouth 1.7–2.3 (vs. 1.3–1.8) times wider than long. It is distinguished further from M. tigrina by having one (vs. two) black spot at the dorsal-fin base, absence (vs. presence) of rows of spots on the pectoral-fin rays, the bar at caudal-fin base dissociated (vs. complete), caudal-peduncle length 10.5–14.0% SL (vs. 15.0–16.0), and pre-dorsal length 47.8–51.8% SL (vs. 45.0–47.0). The new species is further distinguished from M. yunnaniloides by having i+10–11 pectoral-fin rays (vs. i+9), and 9+8 (vs. 8+8) caudal-fin rays. M. daral is distinguished from M. chhimtuipuiensis from the Kaladan drainage by having a complete (vs. incomplete) lateral line, 9–10 regular (vs. 11–14 irregular) set and shaped dark-brown bars on the flank, and 9+8 (vs. 8+7) caudal-fin rays.

Mustura daral is distinguished from M. bella and M. isostigma from the Mekong drainage by having 9–10 regular set and shaped bars on the flank (vs. 12–30 interconnected irregular set and shaped bars separated by a yellow stripe from a middorsal stripe or a series of blotches in M. bella , 5–7 longitudinally elongated blotches in M. isostigma ). It is further distinguished from M. bella by having first branched pectoral-fin ray in the male with (vs. without) small conical tubercles, and presence (vs. absence) of low dorsal and ventral adipose crests on the caudal peduncle. The new species is distinguished from M. isostigma by having a slender caudal-peduncle (depth: 9.7–11.0% SL vs. 8.3–8.6). It is distinguished from M. chulabhornae and M. geisleri from the Chao Phraya drainage by having the saddles on the back continuous with 9–10 regular set and shaped bars on the flank (vs. saddles discontinuous with 8–10 blotches in M. chulabhornae , 5–8 longitudinally elongated blotches in M. geisleri ), and presence (vs. absence) of an axillary pelvic lobe. M. daral is also distinguished from M. chulabhornae by having a complete (vs. incomplete) lateral line. The new species is distinguished from M. maepaiensis and M. shanensis from the Salween drainage by having 9–10 regular set and shaped bars on the flank (vs. 10–13 irregular set and shaped bars in M. maepaiensis , 8 vertically elongated blotches in M. shanensis ). It is further distinguished from M. maepaiensis by having the distal margin of dorsal fin convex (vs. slightly concave), a slender caudal-peduncle (depth: 9.7–11.0% SL vs. 11.5–12.8), and a shorter dorsal-fin (height: 14.4–16.6% SL vs. 16.8–21.7), and from M. shanensis by having pelvic fin not reaching (vs. reaching) the anus, and 9+8 (vs. 8+8) caudal-fin rays.

Figures

FIGURE 1. Mustura daral, a–b. holotype, MUMF 18061, 59.6 mm SL, male (lateral and ventral view). India: Siang River.

FIGURE 2. Mustura daral, paratypes, a–b. MUMF 18063, 64.7 mm SL, male (dorsal and lateral view, left pectoral fin damaged during collection); c. MUMF 18072, 60.7 mm SL, male (lateral view); d. MUMF 18067, 62.6 mm SL, male (lateral view). India: Siang River.

FIGURE 3. Mustura daral, a and d. MUMF 18065, 62.5 mm SL, male; lip structure and head with suborbital flap. Scale bar= 1mm; b–c. MUMF 18068, 56.7 mm SL, male; air bladder and intestine; e. MUMF 18064, 66.8 mm SL, male; pectoral fin. Vertical scale bar = 1 mm. t represents tubercles in the Figure; f. MUMF 18075, 70.4 mm SL, female; pectoral fin.

FIGURE 4. Map showing the type locality of Mustura daral.

FIGURE 5. Siang River at Pasighat, habitat of Mustura daral, India: Siang River.