Physoschistura absumbra, Endruweit, Marco, 2017

Endruweit, Marco, 2017, A new Physoschistura from a Salween affluent in western Yunnan (Teleostei: Nemacheilidae), Zootaxa 4263 (2), pp. 378-386 : 379-385

Physoschistura absumbra , new species

Figs. 1–3

Holotype. KIZ 2014006018 , 39.0 mm SL; China: Yunnan Prov.: Lincang Pref.: Cangyuan Cty.: Banlao town ; Nangunhe River ; 23°10.932' N, 98°56.575' E, elevation 523 m; coll. Endruweit, M. & Qin, T., 23 Aug. 2014.

Paratypes. KIZ 2014006017, 6019 , 6022, 6024, 6026, 6028, 6 specimens, 26.3–43.5 mm SL; ZFMK-ICH 103626-3630, 5, 32.8–39.3 mm SL; same data as holotype.

Diagnosis. Physoschistura absumbra is easily distinguished from all congeners in lacking a suborbital lobe and in having a complete lateral line and a continuous lower jaw. Further diagnostic characters are head depth at nape 13–14% SL; head length dorsally 23–25% SL, laterally 26–28% SL; body depth 15–17% SL; caudalpeduncle depth 13–14% SL; 9–12 rather regular flank bars; basicaudal bar complete; and a maximum adult size of about 44 mm SL.

Description. See Figure 1 for general appearance and Table 1 for morphometric data of the holotype and 10 paratypes. Body compact, predorsally cylindrical, postdorsally laterally compressed. Body depth 5.8–6.7 times in SL, maximum immediately in front of dorsal fin. Caudal peduncle deep, depth 1.0–1.2 times in its length. Axillary pelvic lobe rudimentary, tip free. Anus located 0.9–1.7 times eye diameter in front of anal-fin origin. Snout pointed. Cheek not inflated. Head width constantly increasing from nostril to about edge of preoperculum. Eye large; located dorsolaterally, not reaching dorsal profile when viewed laterally. Interorbital space flat, narrow. Anterior nostril a flap-like tube, not pierced, not reaching orbit. Mouth ( Fig. 2 ) inferior, arched, 1.5–1.8 times wider than long. Lips thick, furrowed close to axis; upper lip not notched, lower lip slightly notched medianly, lateral sides slightly triangular, not forming pads. Upper jaw with pointed processus dentiformis; lower jaw spoon-like, not notched. Inner rostral barbel failing to reach rictus, outer reaching vertical through anterior rim of orbit, maxillary reaching vertical through posterior rim.

Vertebrae 36–38 [37]; 18–19 [19] abdominal and 18–20 [18] caudal (n=8). Gas bladder in ossified capsule; two halves spatially separated, connected via a massive, flattened duct; secondary chamber small, conical, not ossified, in immediate contact with capsule (n=2) ( Fig. 3 ). Gastrointestinal tract with simple, U-shaped stomach; intestines with single bend immediately after stomach. Largest recorded length 43.5 mm SL, 53.6 mm total length (KIZ 2014006022).

Body covered by small, cycloid scales; body in front of dorsal fin and abdomen in front of pelvic fin naked. Lateral line complete, reaching caudal-fin base, with 79–91 pores. Cephalic lateralis system with 7–10 supraorbital, 3+12 infraorbital, 10–11 preoperculo-mandibular and 3 supratemporal pores.

Dorsal fin with 4 simple and 9½–10½ [9½] branched rays; reaching vertical through anal-fin origin; distal margin straight. Anal fin with 3 simple and 5½ branched rays; distal margin convex; not reaching caudal-fin base. Caudal fin deeply emarginate, with 9+8 branched rays; lobes rounded, lower lobe slightly longer. Pelvic fin with 8 rays, reaching anus, inserted about opposite to second branched dorsal-fin ray; fifth ray longest; distal margin convex. Pectoral fin with 11–12 [11] rays, reaching or nearly reaching vertical through dorsal-fin origin; fifth ray longest; distal margin convex.

Coloration of preserved specimens. Body beige-gray, dorsum darker, abdomen lighter, with 9–12 dark gray bars, wider as interspaces; intensity of bars decreasing towards head. Bars straight, rather regular; interconnected over dorsum behind dorsal fin and over ventral midline behind anus; interrupted on caudal peduncle in some specimens. A conspicuous, black humeral spot; a black chevron-shaped stripe along midlateral from caudal-fin base reaching forward to about mid of dorsal fin, absent in some specimens. Bar at caudal-fin base conspicuous, black, straight, complete, not reaching dorsal and ventral extremities. Head gray, top above infraorbital cephalic lateralis canal and upper part of operculum dark gray; lower side with numerous densely set melanophores. Snout with a beige hue. Dorsal fin with a conspicuous, basal, black spot anterior to first branched ray and with a broad, transverse, median black band on light gray ground. Caudal fin with a broad transverse, median, dark gray band on light gray ground. Other fins with a narrow, transverse, dark gray band on light gray ground.

Distribution. Known only from the type locality, a small nameless tributary to the Nangunhe River, Salween drainage ( Fig. 4 ).

Ecology. Obtained from a small tributary, about 2 m wide and 30 cm deep at the collection site, running into the Nangunhe River; could not be obtained from the mainstem of the Nangunhe River. Co-occurring nemacheilids were Schistura cryptofasciata and S. disparizona , both also present in the mainstem.

Etymology. From the mythology of the Wa people, the predominant ethnic minority along the Sinoburmese border in this region. A composite of the Latin words absum, to be absent; and umbra, shadow; an allusion to the Wa’s mythic ancestors, from whom it is said to cast no shadows ( Obayashi 1966). A noun in apposition.

Discussion. Considering the quite high heterogeneity of species currently allocated in Physoschistura there seem to be rather different opinions about its generic definition. Banarescu and Nalbant’s (1982) original generic concept encompasses species with a scaled body, at least posteriorly; an incomplete lateral line, not reaching behind the dorsal fin; a forked caudal fin; 8½–9½ branched dorsal-fin rays; a weak to moderate processus dentiformis; the two halves of the ossified air-bladder capsule merged and coalescent on the inner surfaces lacking a connective duct; a posterior non-ossified air-bladder chamber free in abdominal cavity; and a brownish barred color pattern. By the inclusion of P. elongata in the genus the authors stretched the concept to also accommodate species whose two halves of the air-bladder capsule are not merged but connected via a massive somewhat flattened duct. The peculiar structure of the gas-bladder capsule as present in the genus’ type species, P. brunneana , of two merged halves with their inner surfaces coalescent and thereby making a connective duct-like structure redundant, has not been described from another congener.

Kottelat (1990) argued that the sole presence of a secondary gas-bladder chamber is insufficient to diagnose Physoschistura since some species of other genera also have a secondary chamber, as evidently present in S. similis Kottelat 1990 and Petruichthys brevis ( Boulenger 1893) ( Kottelat 1990) . At least two more Schistura have a secondary chamber; namely S. koladynensis Lokeshwor & Vishwanath 2012 and S. porocephala Lokeshwor & Vishwanath 2013 , both from the Kaladan River. Kottelat (1990, 2001), instead, considered a strongly arched mouth (1.5–2.0 times wider than long) and a conspicuously notched lower lip that forms triangular furrowed lateral pads chief characters to rediagnose the genus. Contradictory, Kottelat et al. (2007) placed a subterranean nemacheilid in Schistura although it possesses the diagnostic peculiar mouth structure. Kottelat (2001) and Chen et al. (2011) do not even list the secondary chamber in their definition of Physoschistura . Following this generic definition several other Schistura would have to be relocated to Physoschistura ; for example S. hoai ( Nguyen 2005) , S. longa ( Zhu 1982) , S. poculi ( Smith 1945) , and S. prolixifasciata Zheng et al. 2012 .

The definition of Physoschistura , as applied by Kottelat (2001) and Chen et al. (2011), is evidently stretched. It is far distant from Banarescu and Nalbant’s (1982) original generic concept and is herein rejected. ‘ Physoschistura’ walongensis Tamang & Sinha 2016 and ‘ P.’ yunnaniloides Chen et al. 2011 cannot be considered congeneric, since they lack the secondary chamber and are, consequently, relocated to Schistura . Apparently, these two species have been described in Physoschistura simply based on the mouth structure. Six more species with a complete (vs. incomplete in the original generic concept) lateral line have been placed in Physoschistura , namely P. chindwinensis , P. prashadi , P. shanensis , P. shuangjiangensis , P. tigrina , and P. tuivaiensis .

The new species, Physoschistura absumbra , is a member of Physoschistura as diagnosed by Banarescu and Nalbant (1982). It also possesses an arched mouth (1.5–1.8 times wider than long) and a notched lower lip, laterally slightly triangular, characters used by Kottelat (1990) to rediagnose the genus.

Physoschistura absumbra is readily distinguished from all congeners in having a complete lateral line, a continuous lower jaw, and in lacking a suborbital lobe. Its occurrence in the Nangunhe River extends the distributional range of the genus further northward (upstream) within the Salween.

The new species somewhat resembles the other Salween species P. brunneana , P. raoi , and P. rivulicola in lacking a suborbital lobe and in having a small reported adult size of less than 44 mm and a barred color pattern but differs from them in having a lower jaw that is not notched (vs. notched in all three species); a complete (vs. incomplete) lateral line; basicaudal bar complete (vs. dissociated); head depth at nape 13–14% SL (vs. 14–17 in P. brunneana ; 15 in P. raoi ; 15–16 in P. rivulicola ); and caudal-peduncle depth 13–14% SL (vs. 9–12; 13; 12–13).

Likewise, P. absumbra shares with the remaining Salween species P. shanensis a small reported adult size of less than 44 mm and, in addition, a complete lateral line. Physoschistura absumbra is readily distinguished from P. shanensis in having a lower that is not notched (vs. notched); a barred (vs. mottled) color pattern; basicaudal bar complete (vs. dissociated); and head length dorsally 23–25% SL (vs. 21), laterally 26–28% SL (vs. 22).

Three valid species of Physoschistura , namely P. chindwinensis , P. prashadi and P. tigrina , have been reported from the drainage of the Chindwin River, a right bank tributary to the Irrawaddy; none from other tributaries nor the mainstem of the Irrawaddy hitherto. The Chindwin River is formed by a network of rivers in the Indoburmese border region and is geographically far distant from the Salween. Physoschistura absumbra shares with the three species occurring in the Chindwin drainage a continuous lower jaw and a complete lateral line. It is easily distinguished from them in lacking (vs. having) a suborbital, having a barred (vs. irregularly barred and blotched) color pattern; HL 23–25% SL (vs. 19–22 in P. chindwinensis ; 22 in P. prashadi ; 19–20 in P. tigrina ); and caudalpeduncle depth 13–14% SL (vs. 9–10; 12; 10–11). Besides, P. tigrina is a large species reaching an adult size of about 74 mm SL (vs. 44 mm SL in P. absumbra ).

Physoschistura absumbra shares with P. chulabhornae from the Chao Phraya drainage and with P. pseudobrunneana and P. shuangjiangensis both from the Mekong a continuous lower jaw, but is distinct from them in lacking (vs. having) a suborbital lobe and having a complete (vs. incomplete in P. chulabhornae and P. pseudobrunneana ; complete in P. shuangjiangensis ) lateral line; HL 23–25% SL (18–23; 21–23; 20–23); caudalpeduncle depth 13–14% SL (vs. 8–12; 11–13 in the latter two); and body depth 15–17% SL (vs. 16–23; 20–22; 18– 21). Besides, the four species differ notably in color pattern: P. absumbra possesses a rather regularly barred pattern whereas it is spotted in P. chulabhornae , irregularly barred or blotched in P. pseudobrunneana , and mottled in P. shuangjiangensis .

Figures

FIGURE 1. Physoschistura absumbra, KIZ 2014006018, holotype, 39.0 mm SL; Yunnan: Cangyuan; Nangunhe River.

FIGURE 2. Physoschistura absumbra, ZFMK-ICH 103627, paratype, 37.6 mm SL; head in ventral view.

FIGURE 3. Physoschistura absumbra, ZFMK-ICH 103627, paratype, 37.6 mm SL; gas bladder.

FIGURE 4. Map of Sino-Burmese border region, taken from Endruweit (2017). Symbol indicates the type locality of Physoschistura absumbra.