Schistura hypsiura, Bohlen & Šlechtová & Udomritthiruj, 2014

Bohlen, Jörg, Šlechtová, Vendula & Udomritthiruj, Kamphol, 2014, Schistura hypsiura, a new species of loach (Cobitoidea: Nemacheilidae) from South-West Myanmar, Raffles Bulletin of Zoology 62, pp. 21-27 : 21-24

Schistura hypsiura , new species

( Figs. 1 , 2 )

Holotype. ZRC 53186, male, 69.1 mm SL; Myanmar: Rakhine State: Kyeinthali Chaung at Ka La Byin , about 17°56'N, 94°30'E; local collector, 8 February 2010.

Paratypes. Same data as holotype, ZRC 53187, 25 , 29.3–72.8 mm SL, 2 specimens cleared and stained. – CMK 21983, 4 , 34.5–72.6 mm SL. – IAPG A4154–4158 , 5 , 26.5 –33.0 mm SL .

Diagnosis. A member of Schistura distinguished from all congeners by: features of its caudal region, including a deep caudal peduncle (as deep or deeper than the deepest part of the body anterior to the caudal peduncle); the absence of dorsal and ventral skin crests along the caudal peduncle; and a deeply forked caudal fin, with the outermost principal rays in the upper and lower lobes more than twice the length of the innermost principal rays. It can be further distinguished by: the presence of a suborbital flap in males; a well-developed suborbital groove in females; and by having 6–8 very regular bars along the body side.

Description. See Fig. 1 for general appearance and Table 1 for morphometric data of holotype and 15 paratypes. Largest specimen examined 72.8 mm SL. Body moderately elongated, only slightly compressed anteriorly, strongly compressed and remarkably high posteriorly (body width at origin of anal fin 5.5–7.2% SL; depth of caudal peduncle 0.8–1.0 times in its length and 0.9–1.1 times in body depth). Maximum body depth either between dorsal-fin base and anal-fin origin or at caudal peduncle. Head width increasing posteriorly between mouth and posterior tip of opercle. Anterior nostril pierced in front side of a flap-like tube, with a low anterior rim. Mouth width about 1.8–1.9 times its length ( Fig. 2 ). Processus dentiformis present, broad, flat. Lips thick. Upper lip with a well-marked median incision; lower lip with a median interruption; both with furrows along entire length. Inner rostral barbel reaching corner of mouth. Outer rostral barbel reaching to base of maxillary barbel. Maxillary barbel reaching vertical through posterior rim of eye. Axillary pelvic lobe present and free. No adipose crest on dorsal or ventral midline of caudal peduncle.

Dorsal fin with three or four simple and 8½ branched rays. Anal fin with three simple and 5½ branched rays, not reaching caudal-fin base. Caudal fin with 9+8 branched rays, deeply forked, length of innermost caudal-fin rays 1.9–2.4 times in length of lower lobe, lobes rounded. Pelvic fins with 7 branched rays; origin opposite branched dorsal-fin ray 1–2; reaching beyond half of distance to anal-fin origin and just behind anus, which is located one eye diameter before origin of anal fin. Pectoral fin with 10–11 branched rays, reaching slightly behind midpoint between bases of pectoral and pelvic fins.

Body completely scaled, including ventral surface; head naked. Lateral line nearly complete, with 82–93 pores, reaching behind vertical through anal-fin origin. Cephalic lateral line system with 6 supraorbital, 4+10 infraorbital, 9 preoperculo-mandibular and 3 supratemporal pores. Both cleared and stained specimens with 35 vertebrae, including 4 vertebrae of Weberian apparatus and ural centrum. Skeleton of caudal peduncle similar to those of other species of Nemacheilidae , but with very broad epural, supporting 3 dorsal procurrent rays dorsally and almost completely filling interneural space between pleurostyle and neural spine of preural centrum 2 ( Fig. 3 ).

Colouration. Ground colour in freshly preserved specimens white to yellowish. Body with 6–8, most commonly 7, dark brown bars reaching ventrally at least to level of pectoral-fin base, and dorsally to dorsal midline, where they join with their antimere. Another bar reaching from middle of opercle to dorsal midline, joining its antimere at nape. Dark brown blotch between eyes on dorsal surface of head. Dark brown Sexual dimorphism. Males exhibit a triangular suborbital flap with a rounded posteroventral tip ( Fig. 4 ). In the largest males (50.3–69.1 mm SL), the suborbital flap exhibits a large lateral extension ( Fig. 4b ). The smallest male specimen examined with this lateral extension is 29.3 mm SL. Females exhibit a suborbital groove ( Fig. 4c ). The smallest female specimen examined with a suborbital groove is 45.2 mm SL. Suborbital flap and groove absent in juveniles. The largest specimen without a suborbital flap or groove is 36.2 mm SL. stripe extending from tip of snout to eye, meeting its antimere at snout. Dark bars broader than interspaces in anterior part of body, decreasing in width posteriorly to become as broad or narrower than interspaces in posterior part of body. Bars generally regular or narrowing ventrally. In some specimens a few bars are y-shaped, irregular or incomplete. In a large specimen (72.8 mm SL), bars in the anterior half of the body exhibit dark brown margins and paler central zones ( Fig. 1h ). Black bar at base of caudal fin interrupted twice; resulting in a black triangle at base of anteriormost dorsal and ventral procurrent fin rays and an elongated black blotch at center of caudal-fin base. Blotch at center of caudal-fin base much thinner than body bars; its depth 5.8–8.4% SL and width 2.3–3.8 times in its depth. All three parts of this black bar are clearly visible in juveniles. In adults a deeper dark brown bar is present across entire caudal-fin base, making components of the black bar less visible.

Dorsal fin with one to three dark brown elongated blotches at base and a prominent row of round or elongated dark brown dots at 2/3 of fin height in association with fin rays. In small specimens, dark brown dots are located at the first branching point of the branched dorsa-fin rays or slightly distal of the first branching point. In larger specimens, dark brown dots are located more distal to the first branching point of the branched dorsal-fin rays or at the level of the second branching point in the largest specimens. Caudal fin either pale, with small scattered dots or with one to four dark brown bars. Anal fin either hyaline or with one or two indistinct dark brown stripes. Pelvic and pectoral fins either hyaline or with irregular dark brown pigmentation along rays.

Distribution. Presently known only from the type locality ( Fig. 5 ).

Etymology. From the Greek hypsos, meaning high, and oura meaning tail; referring to the high caudal peduncle. An adjective.

Figures

Fig. 1. Schistura hypsiura, Myanmar, Rakhine state: Kyeinthali Chaung, a, b, ZRC 53186, holotype, male 69.1 mm SL; c–g, ZRC 53187; c, male 48.4 mm SL; d, male 48.7 mm SL; e, male 58.2 mm SL; f, female 48.2 mm SL; g, female 51.1 mm SL; h, female 72.8 mm SL.

Fig. 2. Schistura hypsiura, Myanmar, Rakhine state: Kyeinthali Chaung, ZRC 53186, holotype, male, 69.1 mm SL. Mouth in ventral view.

Fig. 3. Schistura hypsiura, ZRC 53187, 49.1 mm SL: caudal skeleton. cc = compound centrum; ep = epural; ipc = innermost principle caudal-fin rays; pc2 = preural centrum 2; pc3 = preural centrume 3; pl = pleurostyle.

Fig. 4. Sexual dimorphism in Schistura hypsiura: a, ZRC 53487, paratype, 50.2 mm SL; suborbital flap of a small male; b, ZRC 53186, holotype, 69.1 mm SL, suborbital flap of a large male; c, ZRC 53187, paratype, 72.8 mm SL, suborbital grove of a female. Scale bar = 1 mm.

Fig. 5. Map of Myanmar and surrounding areas. Type locality of Schistura hypsiura in southern Rakhine State is indicated by an X.