Schistura larketensis, Choudhury & Mukhim & Basumatary & Warbah & Sarma, 2017

Choudhury, Hrishikesh, Mukhim, D. Khlur B., Basumatary, Sudem, Warbah, Deisakee P. & Sarma, Dandadhar, 2017, Schistura larketensis, a new cavernicolous fish (Teleostei: Nemacheilidae) from Meghalaya, Northeast India, Zootaxa 4353 (1), pp. 89-100 : 90-94

Schistura larketensis , new species

( Figs. 1 & 2 )

Holotype. GUMF 0 261, female, 54.5 mm SL; India: Meghalaya: East Jaintia Hills District: Krem Khung about 1.5 km from Larket village (25°23ʹ22ʺ N, 92°34ʹ49ʺ E; 880 m above sea level); D. K. B. Mukhim & party, 24 February 2016.

Paratypes. GUMF 0262/3, 3 specimens, 41.0– 54.7 mm SL; same data as holotype. GUMF 0263 /2, 63.1–68.1 mm SL, 2 specimens ; same locality as holotype; D.K.B. Mukhim & party, October 2012. GUMF 0264 /3, 3 specimens, 49.6–61.3 mm SL ; same locality as holotype; D. K. B. Mukhim & party, 30 October 2016. ZSI FF7225, 60.4 mm SL ; same data as holotype.

Diagnosis. Schistura larketensis is distinguished from its congeners in possessing a combination of the following characters: a pale to weakly-pigmented body; a thick and short basicaudal bar immediately below the lateral-line scale row (often appearing broken in some individuals); the eyes vestigial or absent; a smooth ventrolateral surface of the head; the anterior nostrils forming long and pointed triangular tube-like flaps; an incomplete lateral-line; a small and cylindrical, axillary pelvic-lobe; the chest naked; and an emarginated caudal-fin.

Description. Figure 1 illustrates the general appearance and Table 1 presents the morphometric data for the holotype and nine paratypes. Body moderately elongate, nearly circular in cross-section anteriorly to dorsal-fin origin, compressed posteriorly. Head depressed at nape, its anterior profile rising evenly above nares. Dorsal body profile gently rising, appearing almost straight up to dorsal-fin origin, then descending slightly along dorsal-fin base, then straight up to caudal-fin base. Mouth semi-circular, about 1.2–1.6 times wider than long, with thick, fleshy, pleated lips; upper lip with small median incision (absent in specimens below 54.7 mm SL); lower lip with wide median incision, its median lobes with 5–8 well marked furrows; rest of lip plain ( Fig. 3a ). Broad, flat processus dentiformis present on upper jaw, with corresponding shallow median concavity on lower jaw. Eyes, when present, vestigial, subcutaneous, absent in larger specimens (above 63.1 mm SL). Anterior nostrils pierced in front of long and pointed tube-like flaps, not reaching (vestigial) eyes. Barbels in three pairs: inner rostral barbels reaching angle of mouth, outer rostral and maxillary barbels reaching anterior margin of (vestigial) eyes.

Dorsal-fin with four simple and 8 (n = 1) or 8½ (n = 9) branched rays, its origin slightly ahead of pelvic-fin origin. Anal-fin with three simple and 5 (n = 1) or 5½ (n = 9) branched rays, fin not reaching caudal-fin base. Caudal-fin with 9 + 8 (n =10) branched rays, deeply emarginated, upper lobe about 1.0–1.1 times longer than lower, both lobes with broadly pointed tips. Pelvic-fin with 6 (n = 1) or 7 (n = 9) branched rays, reaching anus when adpressed (except in specimens below 54.7 mm SL); its origin vertically below second branched dorsal-fin ray. Pectoral-fin with 10 (n = 8) or 11 (n = 2) branched rays, reaching about midway between bases of pectoral and pelvic fins. Anus situated posteriorly, nearer to anal-fin origin, about ⅔ pelvic-anal distance from pelvic-fin origin.

Body entirely covered by minute deeply-embedded cycloid scales, except on head, and chest between pectoral fins. Lateral-line incomplete, reaching vertical through first, fourth or last branched ray of dorsal-fin, with about 27–38 pores (pores indistinct, hence difficult to count). Cephalic lateralis system consists of 7 supra-orbital, 4 + 7– 9 infra-orbital, 10–11 pre-operculomandibular, and 3 supra-temporal pores. Intestine with small loop behind posterior end of stomach ( Fig. 3b ). Air bladder without any free posterior chamber ( Fig. 3c ). Lips, barbels covered by numerous unculi. Axillary pelvic lobe present, small, cylindrical, deciduous (detached from some specimens). Short and shallow adipose crests on dorsal and ventral midline of caudal peduncle. Vertebrae: 37.

Coloration. In preservative ( Fig. 1a–i ): Colour pattern variable (possibly due to age variation or preservation). In two specimens (54.5 mm SL; 53.4 mm SL; Fig. 1a, f ), ground colour dull-beige to light-cream with dorso-lateral half (about ½ or ⅔) of body darker beige to dull brownish. Head and cheeks darker, with much lighter nasal flaps. Barbels dull-brown. Two faded dorsal and four or five post-dorsal saddles continue as indistinct, irregular bars, usually wider than interspaces, reaching up to two-third of lateral half of body. Black spot at base of simple and first branched dorsal-fin rays; faint blackish stripe along entire dorsal-fin base, from third branched ray. Faded, short, thick, incomplete black caudal bar present below lateral-line scale row. In the holotype ( Fig. 1a ), caudal bar reaching upper end of caudal-fin base, broken midway along level and slightly above lateral-line. Caudal-fin with faint, oblique brownish bars towards bases; additional irregular markings on fin rays. Vertically elongate, brownish blotch immediately above pectoral-fin base below lateral-line, behind operculum, partly covering cleithrum. Proximal two-thirds of pectoral and dorsal-fin rays with faint black coloration. Pelvic, anal fins hyaline.

In some specimens, ground colour faded beige to creamy-white with slightly darker dorso-lateral half. Faint black spot at base of simple and first branched dorsal-fin rays sometimes present (61.3 mm SL, Fig. 1g ; 49.6 mm SL). Faint brownish caudal bar below lateral-line scale row. Caudal-fin with faint oblique grayish marks. Dorsal aspect of pectoral and dorsal-fin rays with faint brownish colour. Four or five pale brownish post dorsal saddles sometimes present. In one individual (49.6 mm SL; Fig. 1e ), faint blackish-brown blotches aggregate to give appearance of a stripe along lateral-line, more distinct towards posterior end. In another individual (60.4 mm SL, Fig. 1h ), several light brown bars present below lateral-line; barbels dull white. In large specimens (68.1 mm SL, Fig. 1i ; 63.1 mm SL), overall body coloration faded beige to dull white, with faint remains of caudal bar and blotch above pectoral base. Fins hyaline except for faint brownish markings on caudal-fin lobes. Barbels dull-white.

In juveniles (41.0 mm SL, Fig. 1d ; 45.1 mm SL): Ground colour dull white, with darker dorso-lateral half. Three dorsal and five post-dorsal saddles present, together with narrow mid-lateral stripe (apparently an aggregation of blotches) along entire body length present. Caudal bar short, thick, just below lateral-line scale row. Caudal-fin with oblique brownish marks. Barbels dull-white.

Coloration in life ( Fig. 2 ): Ground colour pinkish beige. About ⅔ of dorso-lateral half of body brownish with aggregated melanophores, anterior half darker than posterior. Chest, abdomen whitish with thin translucent skin. Vertical brownish blotch behind operculum, below lateral-line; short, thick, faint brownish basicaudal bar below lateral-line scale row; dark brownish-black spot at base of simple and first branched dorsal-fin rays; faint blackish stripe along entire dorsal-fin base from third branched ray present. Eyes appear as black spots below thin layer of transparent skin. Two dark-brownish dorsal and four post-dorsal faint saddles continue as bars, much darker along mid-lateral half of body, appearing as blotches. Fins hyaline, except for faint brownish to blackish markings on dorsal-fin rays, towards base of caudal-fin lobes, and in dorsal aspect of bases of pectoral and pelvic-fin rays. Barbels dark-pink.

Notes on biology. One dissected paratype (GUMF 0263/2, 63.1 mm SL), a ripe female, contained about 250 eggs with an approximate diameter of 0.6 mm. Dissection of the stomach revealed no identifiable remains.

Sexual dimorphism. No apparent external dimorphism. The sex of the holotype could be determined, however, while it was alive, with ripe eggs easily visible through its thin translucent belly.

Distribution. Presently, the species is known only from Krem Khung, located about 1.5 km from the Larket Village, East Jaintia Hills District, Meghalaya, India ( Fig. 4 ).

Habitat. The new species was collected from a small stagnant pool a few square meters in area and about 1 m in depth, located in a wet passage some 500 m from the main entrance of Krem Khung. The pool bed is mostly sandy with scattered pebbles ( Fig. 5 ). The water was clear, pH 8.6, and a very low D.O. of 1.1 ppm when analyzed in the month of April 2015. No other macrofauna were recorded inside the cave except weakly-pigmented crabs and crayfish, crickets, cockroaches and millipedes.

Etymology. The species name is derived from the ‘Larket’ village, the locality of Krem Khung. This name is proposed so as to encourage the village to take up biodiversity conservation as it is already in the process of constituting a Biodiversity Management Committee under the Indian Biodiversity Act.

Figures

FIGURE 1. Schistura larketensis, India: Meghalaya: Krem Khung; a–c, holotype, female, GUMF 0261, 54.5 mm SL, lateral, dorsal and ventral views; d, paratype, GUMF 0262/3, 41.0 mm SL; e–g, paratypes, GUMF 0264/3, 49.6 mm SL, 53.4 mm SL, 61.3 mm SL; h, paratype, ZSI FF7225, 60.4 mm SL; i, paratype, GUMF 0263/2, 68.1 mm SL.

FIGURE 2. Live colouration of Schistura larketensis, GUMF uncat, about 52 mm SL; India: Meghalaya: Krem Khung.

FIGURE 3. Illustrations showing: a, lip structure; b, air bladder; and c, digestive tract of Schistura larketensis. Scale bars 1 mm.

FIGURE 4. Map showing the collection locality of Schistura larketensis (filled circle) and the type locality of S. papulifera (filled square).

FIGURE 5. Photograph showing water pool in Krem Khung, the habitat of Schistura larketensis.