Mustura taretensis, Chinglemba & Rameshori & Vishwanath, 2021

Chinglemba, Yengkhom, Rameshori, Yumnam & Vishwanath, Waikhom, 2021, A new species of stone loach of the genus Mustura (Teleostei: Nemacheilidae) from Chindwin River drainage, Manipur, north-eastern India, Zootaxa 5081 (4), pp. 551-565 : 552-558

Mustura taretensis , new species

( Fig. 1 )

Holotype. MUMF 18007 , 52.0 mm SL, female; India: Manipur: Tengnoupal District: Taret River ( Chindwin River drainage); 24°29'55"N 94°22'39"E, 242 m asl; Yengkhom Chinglemba et al., 10 March 2018.

Paratypes. MUMF 18008–18009 , 2 ex., 46.6–49.9 mm SL, females ; MUMF 18010 , 1 ex., 45.9 mm SL, male ; MUMF 18011–18017 , 7 ex., 38.8–43.7 mm SL, females ; MUMF 18018–18019 , 2 ex., 50.5–51.7 mm SL, males ; MUMF 18020–18023 , 4 ex., 40.4–46.9 mm SL, females ; MUMF 18024–18029 , 6 ex., 46.8–50.6 mm SL, males; same data as holotype .

Diagnosis. Mustura taretensis is distinguished from all other known species of Mustura by a combination of the following characters: body with 12–13 irregular dark-brown blotches or bars on flank, alternately arranged with 11–16 dark brown saddles of varying shape and size on the back; dorsum of head with a distinct rhomboid darkbrown mark encircling a pale oval area on the nape; basicaudal bar black, its dorsal extremity presenting as a small, slightly oblique blotch, its ventral extremity presenting as a vertically elongated blotch, more or less connected by an indistinct black region between the two; dorsal fin with 9½­ or 10½­ branched rays; caudal fin with 9+8 or 8+8 or 8+7 branched rays; lateral line complete; axillary pelvic lobe present; processus dentiformis poorly developed; suborbital flap present in male; and body depth 12.8–16.0 % SL.

Description. General appearance as in Fig 1 . Morphometric data of holotype and 22 paratypes are presented in Table 1. A medium-sized nemacheiline, with moderately elongate, slender body. Body slightly depressed anteriorly, compressed posteriorly. Dorsal profile of body arched, elevating gently from tip of snout to nape, then evenly to dorsal-fin origin, sloping gently to point vertical to anal-fin origin, then straight to caudal-fin base. Body depth greatest at dorsal-fin origin. Behind dorsal fin, body depth gradually decreasing to caudal-fin base. Ventral profile of body slightly convex but more or less straight up to anal-fin origin, then inclined evenly towards caudal-fin base. Head depressed, triangular, 1.0–1.1 times wider than deep. Snout slightly blunt, short, rounded, its length about two-fifths dorsal head length. Maximum head width 2.0–2.7 times interorbital width.

Dorsal fin with 3 (23) simple and 9½­* (16) or 10½­ (7) branched rays, its origin midway between tip of snout and caudal-fin base, anterior to pelvic-fin origin.Anterior margin of dorsal fin convex, distal margin almost straight. Anal fin with 3 (23) simple and 5½­ (23) branched rays, last ray not reaching caudal-fin base when adpressed. Pectoral fin with 1 (23) simple and 10* (12) or 11 (11) branched rays, reaching about two-thirds of distance to pelvic-fin origin. Pelvic fin with 1 (23) simple and 7 (23) branched rays, its origin under branched dorsal-fin ray 2 or 3, reaching anus when adpressed. Axillary pelvic lobe present. Caudal fin with 9+8* (19) or 8+8 (2) or 8+7 (2) branched rays, deeply emarginated, lobes subequal, lower lobe slightly longer than upper. Caudal peduncle 1.2–1.7 times longer than deep, with low dorsal and ventral adipose crests on posterior half. A prominent dimple-like depression on lateral line on caudal peduncle. Largest recorded size 52.0 mm SL (MUMF 18007).

Body entirely covered with minute, deeply embedded scales, including belly, except on chest and head; posterior to chest, density of scales gradually increases to caudal fin base. Lateral line complete, with 83–92 pores. Cephalic lateral line system with 7* (21)–8 (2) supraorbital, 4+9* (6)–10 (17) infraorbital, 8*–10 preoperculo-mandibular and 3 (23) supratemporal pores. Lips and barbels with unculi.

Anterior nostril pierced at front of low, leaf-like tube. Mouth moderately arched, about 1.3–1.8 times wider than long ( Fig. 2 ). Lips thin, fleshy. Lower lip with a well-marked median interruption, each half forming more or less triangular ‘cushion’, a few furrows on each side, tip of jaw exposed; the two halves orientated in an acute angle. Upper lip with small median incision, thicker at edges. Furrows on the upper lip regularly arranged. No median notch in lower jaw. Processus dentiformis present, poorly developed. Barbels three pairs, long. Inner rostral barbel reaching vertical through middle of eye, its length two-thirds that of maxillary barbel; outer one reaching beyond maxillary barbel base. Maxillary barbel reaching vertical slightly beyond posterior margin of eye. Free posterior chamber of air bladder small, not encapsulated, spherical, concealed beneath manubrium connecting the two halves of air blad- der ( Fig.3a ). Intestine with a small loop a short distance from the stomach ( Fig. 4 ). Total vertebrae 34 (2).

Sexual dimorphism. Males with prominent angular suborbital flap with a slightly blunt tip, small tubercles present on its edges ( Fig. 5a ). In males, pectoral fin slanted, directed slightly upwards, first branched ray longest, falcate, rigid, about three times wider than other branched rays, branched once, without membrane between branches except near tip; unculiferous pad present on dorsal surface of pectoral-fin rays, with small conical tubercles sparsely distributed dorsally among melanophores on inner edge of first branched ray ( Fig.6a ), similar tubercles sparsely on inner edge of second branched ray. These secondary sexual characters are absent in females ( Fig. 6f ). In females, second branched pectoral-fin ray longest.

Coloration. After fixation in 10% formalin, body with 11–16 dark brown saddles on the dorsal midline (3–5 pre-dorsally, 3–4 sub-dorsally, 5–7 post-dorsally). Saddles on both dorsal-fin base and behind it irregular in shape, becoming wider and slightly more extended on flank. Pre-dorsally, a single row of vertically or obliquely elongated bars of variable size and shape arranged more or less regularly or irregularly on side of body between saddles and blotches or bars touching lateral line on flank, alternating with the mid-dorsal saddles and blotches or bars on flank in most examples. In some specimens, a few saddles on and behind dorsal-fin base, fused with blotches or bars on flank. Flank with 12–13 irregular dark-brown blotches or bars, alternately arranged with saddles (or predorsal bars present between saddles and mid-lateral blotches or bars), interspaces about ¾ width of each bar or blotch.

Shape, size and pattern of saddles and bars on body show slight variations among the specimens ( Fig. 7 ). Body background colour pale cream on dorsum and side, densely populated with melanophores; ventrally dull white, without melanophores except near anal fin. Head background dorsally pale yellow, dotted with melanophores; dorsum of head with a distinctly visible rhomboid dark-brown mark encircling a pale oval area on nape, the mark either continuous or formed by 4–6 blotches with faint narrower colouration between blotches ( Fig. 8 ), anterior edges extending forward to interorbital space; lateral portion pale yellowish, with melanophores; pale yellowish ventrally, with melanophores near the lower lip. Nostril encircled by dark-brown pigment, extending forward in parallel towards snout, separated by a spot near tip of snout. Outer and inner rostral barbels with melanophores; maxillary barbel dull white, with melanophores only at base.

Basicaudal bar black, with a small, slightly oblique blotch close to its dorsal extremity and a vertically elongate blotch close to its ventral extremity, connected by a faint blacking region between the two; blotches not reaching upper and lower extremities of bar; upper blotch superimposed on posterior dorsal procurrent rays, base of principal simple ray and 1–4 upper branched rays; lower blotch superimposed on base of all lower branched caudal-fin rays, ventral principal ray and anterior ventral procurrent rays.

Dorsal fin hyaline, with melanophores on rays; a black spot at bases of simple and first branched rays of dorsal fin; two rows of black spots touching the last simple and all the branched rays of dorsal fin, one approximately midway on branching points of branched rays, the other a little above first one, closer to distal margin. Pectoral and pelvic fins hyaline, with pigments on rays. Anal fin hyaline, with scattered melanophores on interradial membrane. Caudal fin dusky, with scattered melanophores; two rows of black V-shaped spots on distal margin, touching all branched rays, with vertices pointed towards caudal-fin base.

Notes on biology. The two dissected females (MUMF 18016–18017, 38.8–41.8 mm SL) have unripe ovaries. The stomachs in both examples contain unidentifiable vegetable matter.

Distribution and Habitat. Presently known only from the Taret River, at the vicinity of Saibol Village, Tengnoupal District, Manipur, India, a tributary of the Yu River, Chindwin River drainage, near the Indo-Myanmar border ( Fig. 9 ).

The new species inhabits cool, clear, swift-flowing freshwater streams over a substrate of gravel, cobble and boulders covered in lush green algal growth ( Fig. 10 ). The type series was collected from shallow clearwater regions of depth ~ 0.5–0.8 m. Other species occurring with Mustura taretensis were, Cyprinidae : Neolissochilus paucisqamatus , Opsarius dogarsinghi , O. ngawa ; Botidae: Botia histrionica ; Nemacheilidae : Schistura rubrimaculata ; Sisoridae : Glyptothorax trilineatus ; and Bagridae : Batasio affinis .

Etymology. The species is named after the Taret River, its type locality. An adjective.

Figures

FIGURE 1. Mustura taretensis, sp. nov., holotype, female, MUMF 18007, 52.0 mm SL; a. lateral, b. dorsal and c. ventral views. India: Manipur: Tengnoupal District: Taret River (Chindwin River drainage).

FIGURE 2. Lip structure of Mustura taretensis, sp. nov. (MUMF 18007, 52.0 mm SL).

FIGURE 3. Air bladder of a. Mustura taretensis, sp. nov. (MUMF 18017, 41.8 mm SL); b. M. dikrogensis (MUMF 11092, 36.6 mm SL).

FIGURE 4. Coiling pattern of intestine of Mustura taretensis, sp. nov. (MUMF 18016, 38.8 mm SL).

FIGURE 5. Lateral view of head of males of a. Mustura taretensis, sp. nov. (MUMF 18010, 45.9 mm SL); b. M. chindwinensis (MUMF 11077, 43.3 mm SL); c. M. dikrongensis (MUMF 11092, 36.6 mm SL); d. M. tigrina (MUMF 11051, 73.6 mm SL) and e. M. tuivaiensis (MUMF 5086, 40.9 mm SL), showing suborbital flap.

FIGURE 6. Pectoral fin of male of a. Mustura taretensis, sp. nov. (MUMF 18018, 50.5 mm SL); b. male of M. chindwinensis (MUMF 11074, 39.68 mm SL); c male of M. dikrongensis (MUMF 11092, 36.6 mm SL); d. male of M. tirgina (MUMF 11051, 73.6 mm SL); e. male of M. tuivaiensis (MUMF 5086, 40.9 mm SL), showing wider first branched rays and tubercles and f. female of M. taretensis, sp. nov. (MUMF 18011, 43.7 mm SL), showing unexpanded first branched ray.

FIGURE 7. Coloration of Mustura taretensis, sp. nov., paratypes: a. female, MUMF 18009, 46.6 mm SL, b. female, MUMF 18014, 40.1 mm SL.

FIGURE 8. Dorsum of head of Mustura taretensis, sp. nov., showing dark brown rhomboidal mark on nape a. holotype, female, MUMF 18007, 52.0 mm SL; b. paratype, female, MUMF 18009, 46.6 mm SL.

FIGURE 9. Map showing the type localities of Mustura species in the Chindwin-Irrawaddy River drainage: 1. Mustura celata, 2. M. chindwinensis, 3. M. prashadi, 4. M. shuensis, 5. M. tigrina, 6. M. yunnaniloides and 7. M. taretensis, sp. nov.

FIGURE 10. Image showing habitat of Mustura taretensis, sp. nov., in Taret River, Manipur, India.