Schistura falamensis, Chen & Myint & Chu & Chen, 2020

Chen, Meng-Fang, Myint, Khin Mar, Chu, Ling & Chen, Xiao-Yong, 2020, Two new species of loaches from the Irrawaddy River basin, Chin State, Myanmar (Teleostei: Cypriniformes: Nemacheilidae), Zootaxa 4895 (1), pp. 86-102 : 87-94

Schistura falamensis sp. nov.

( Fig. 1 )

Holotype. KIZ 2018002396 , 35.9 mm SL, male, Myanmar: Chin State: Falam District, main channel of Manipur River, 22°57’48” N, 93°41’1” E, 320 m elevation, Paing Zaw , Nay Htet Naing , 24 March 2018.

Paratypes. KIZ 20018002397–2399 , SEABRI 20181108, 20191137, 24.7–37.1 mm SL; 5 ex., collected with holotype; SEABRI 201902692–96, 31.8–37.3 mm SL, 5 ex., tributary of Manipur River at Vvar bridge, Chin State, Myanmar, XY. Chen , Nay Htet Naing , Khin Yadanar Htay , Nyein Chan, and Salai Myoe Myin Oo, 9 November 2019 .

Diagnosis. Schistura falamensis sp. nov. can be distinguished from all other species of Schistura occurring in the Irrawaddy River basin by a combination of the following characters: 5–8 blackish brown bars on flank; indistinct bars in front of dorsal-fin origin; bars on posterior part of body regular, twice as wide as interspace; black basal caudal bar dissociated, short, not reaching ventral; lateral line complete; males with suborbital flap; and processus dentiformis undeveloped.

Description. General appearance and morphometric data of holotype and paratypes are shown in Fig. 1 and Table 1, respectively.

Body moderately elongated, with body depth increasing gradually to point in front of dorsal-fin origin, decreasing under dorsal fin, and straight to base of caudal fin. Head pointed, triangular in ventral view. No adipose crest on dorsal midline of caudal peduncle between dorsal fin and caudal-fin base. Largest known size 37.1 mm SL.

Dorsal fin with 3 simple and 7½–8½ branched rays. Dorsal distal margin of dorsal fin slightly convex. Pectoral fin with 1 simple and 8 branched rays, slightly falcate, reaching halfway to base of pelvic fin. No proper axillary pectoral lobe but bulge present dorsally at base of fin. Pelvic fin with 1 simple and 6 branched rays; reaching one half to two thirds of distance to anal-fin origin, not reaching anus, situated about 1.5 eye diameters in front of anal-fin origin. Developed axillary pelvic lobe present. Anal fin with 3 simple and 5½ branched rays, not reaching caudal-fin base. Caudal fin deeply forked, with rounded tip and, 9+8 branched rays.

Body covered with embedded scales, except on thorax and abdomen. Lateral line complete, 78–85 pores. Cephalic lateral system with 6 supraorbital, 4+10 infraorbital, 9 preoperculo-mandibular, and 3 supratemporal pores.

Anterior nostril pierced on front side of flap-like tube, anterior margin with deep concave and tip of flap pointed. Mouth arched, twice as wide as long ( Fig. 2 ). Upper lip with small median incision, 1–2 shallow furrows in median area on each side, lateral area smooth. Processus dentiformis present, narrow, weak. Lower lip with median interruption and 3–5 deep furrows in median area on each side.Anterior rostral barbel reaching mouth corner. Rostral barbel just surpassing base of maxillary barbel. Maxillary barbel longer, reaching vertical of posterior margin of eye, its length almost equal to width of mouth. Intestine with small loop some distance behind stomach ( Fig. 3 ). Gill rakers 10-10 (1).

Sexual dimorphism. Males possess semicircular suborbital flap ( Fig. 4 ). Females possess suborbital groove ( Fig. 5 ).

Coloration (preserved in formalin). Ground color in preserved specimens light gray. Upper dorsal and body dark brown, lower body pale yellow. Thorax and abdomen hyaline in ventral view. From nape to dorsal-fin origin light brown, with 4–5 wide brown saddles on dorsal midline of dorsal-fin base to caudal fin base. Brown bars from opercle to dorsal-fin origin indistinct; bars connected at dorsal midline. At 36.7 mm SL, bars indistinct in front of dorsal-fin origin. At 31.2 mm SL, bars in front of dorsal-fin origin divided into two thin vertical ones. At 26.1 mm SL, bars connected in front of dorsal-fin origin ( Fig. 6 ). 4–6 distinct, regular brown bars under and behind base of dorsal fin, twice as wide as interspace, extending to pelvic fin in ventral and dorsal midline. Bars usually connected on ventral side of body, more prominent on caudal peduncle. Black basal caudal bar at base of caudal fin thin, disassociated into small dorsal dot, which usually reaches dorsal midline, and ventral bar, which does not reach ventral extremity. 3 black blotches above dorsal midline on dorsal-fin base, stretching to base of last unbranched and first branched ray, 4 th– 6 th branched rays, and last two branched rays, respectively. Row of dark blotches stretching across middle third of dorsal-fin ray. Row of vertical dots across middle of caudal fin, forming transverse V-shaped band. Other fins hyaline, axial two thirds of caudal fin rays grayish.

In life ( Fig. 7 ): most of body dark brown and ventral pale yellow. First unbranched and branched dorsal fin orange-red with row of black spots on median dorsal fin. Caudal fin with black pigment, outermost unbranched fin orange-red; pectoral, anal, and pelvic fins pale yellow with several light gray spots.

Distribution and habitat. Schistura falamensis sp. nov. is presently known only from the Manipur River drainage surrounding Falam District, Chin State, Myanmar ( Fig. 8 ). Manipur River is a medium fast-flowing river ( Fig. 9 ), which was 50 m wide and 2 m deep at the time of second sampling in November. The water of the Manipur River tributary is clear, and the riverbed is rocky and sandy, with dissolved oxygen 6.8 mg /L, water temperature 22.4 °C, pH 8.5, and conductivity 277 μs/m.

Etymology. The noun falam refers to Falam District, Chin State, Myanmar, the type locality of the species. Falam means “refuge for children” in the local Chin language.

Remarks

According to the identification key of Schistura in Kottelat (1990) , Schistura falamensis sp. nov. appears to be most similar to S. prashadi (Hora 1921) from the Irrawaddy River basin in Manipur State, India, S. maepaiensis ( Kottelat 1990) from the Salween River basin in Thailand, and S. desmotes (Fowler 1934) from the upper Mae Nam Ping and Mae Khlong river basins in Thailand. Nemacheilus prashadi Hora 1921 was initially identified as Schistura by Kottelat (1990) but was later transferred to the genus Physoschistura Bănărescu & Nalbant 1982 by Lokeshwor & Vishwanath (2012) and recently tentatively placed in Mustura together with S. maepaiensis by Kottelat (2018). The characteristics of Schistura are mouth moderately arched, lower lip with median interruption, but not forming two lateral triangular pads; and no free posterior chamber of air bladder ( Kottelat, 1990). Mustura can be diagnosed based on several characters not found in the new species, namely: male pectoral fin with first branched ray wider than following rays, branched once, branches close together, without membrane between them except near tip, and tiny, circular posterior air bladder ( Kottelat, 2018). Furthermore, morphologically similar genera, such as Nemacheilus , can be distinguished by no median interruption in lower lip; enlarged scales possibly present above and below lateral line; acuminate scales may be present above and below lateral line on caudal peduncle ( Kottelat, 1990). Thus, based on the absence of a posterior air bladder and usual presence of median interruption in lower lip, Schistura falamensis sp. nov. can be confidently placed in the genus Schistura .

Schistura falamensis sp. nov. can be distinguished from S. desmotes by black basal caudal bar dissociated (vs. continuous); upper and lower lips with furrows (vs. without); 1 row of dark spots at dorsal fin rays (vs. 2); bulge present dorsally at base of pectoral fin (vs. absent); and processus dentiformis weak (vs. well-developed).

Sixteen species of Schistura have been described from China and Myanmar in the Irrawaddy River basin. Schistura falamensis sp. nov. shares no crest on caudal peduncle and 9+8 branched caudal rays with S. malaisei and S. megalodon , but differs from S. malaisei by suborbital flap in males present (vs. absent) and lateral line complete (vs. incomplete), and from S. megalodon by black basicaudal bar disassociated (vs. broad and distinct basicaudal bar with forward extensions). Schistura falamensis sp. nov. shares disassociated basicaudal bar and 7 branched dorsal rays with S. albirostris but can be distinguished by lateral line complete (vs. incomplete), suborbital flap in males present (vs. absent), and 9+8 branched caudal rays (vs. 8+8). Schistura falamensis sp. nov. shares forked caudal fin and 9+8 branched caudal rays with S. callidora but can be distinguished from S. callidora by no crest (vs. prominent adipose crest on caudal peduncle) (adipose crest 15–19 % of caudal peduncle depth). Schistura falamensis sp. nov. can be easily distinguished from S. acuticephala , S. indawgyiana , S. nubigena , S. paucifasciata , and S. pawensis by their unique color pattern. It can be further distinguished from S. acuticephala , S. nubigena , and S. paucifasciata by lateral line complete (vs. incomplete) and suborbital flap in males present (vs. absent). Schistura falamensis sp. nov. differs from S. indawgyiana by 9+8 branched caudal rays (vs. 7+7), from S. pawensis by 9+8 branched caudal rays (vs. 7–8+8), absence of stripe on body (vs. prominent black mid-lateral stripe); and no adipose crest on caudal peduncle (vs. small adipose crest present).

Schistura falamensis sp. nov. shares suborbital flap in males with S. polytaenia , S. rubrimaculata , S. sikmaiensis , S. wanlainensis , and S. yingjiangensis , and thus can be readily distinguished from S. puncticeps and S. vinciguerrae . It can be further distinguished from S. puncticeps by head covered in tiny dark dots (vs. large dark brown blotches); 5–8 vertical bars on body (vs. 5–8 large brown blotches); back with 4–5 wide brown saddles (vs. 6–8 dark brown saddles); black basal caudal bar dissociated, short, not reaching ventral (vs. dissociated), equal semicircle; pelvic fin not reaching anus (vs. reaching); both lips with furrows (vs. without); suborbital flap present (vs. absent); and caudal fin deeply forked (vs. deeply emarginate). It can be further distinguished from S. vinciguerrae by head pointed (vs. nearly circular section); pelvic fin not reaching anus (vs. reaching or slightly beyond); head longer (lateral head: 3.6–3.9 times SL vs. 4.5–5.9); and distance from base of dorsal fin to mouth half of standard length (vs. 40–50%).

Schistura falamensis sp. nov. can be distinguished from S. polytaenia by 5–8 vertical bars on body (vs. 19–30); and caudal fin deeply forked (vs. slightly emarginate).

Schistura falamensis sp. nov. can be distinguished from S. rubrimaculata by moderately elongated body (vs. slender); ventral half of head and body dark (vs. white); body without stripe (vs. body with prominent black midlateral stripe); upper lip with furrows (vs. without); red dot absent (vs. distinct red dot present on side of caudal peduncle, in life); and dark blotch stretched across middle third of dorsal-fin rays (vs. absent).

Schistura falamensis sp. nov. can be distinguished from S. sikmaiensis by processus dentiformis present (vs. absent); 5–8 vertical bars on body (vs. 17–20); basal caudal bar dissociated (vs. complete); and 9 pectoral fin rays (vs. 11).

Schistura falamensis sp. nov. can be distinguished from S. wanlainensis by body depth at dorsal-fin origin almost equal to depth of caudal peduncle (vs. body depth twice depth of caudal peduncle); head pointed (vs. slightly depressed); 5–8 black brown bars on body (vs. 18–32); bars behind dorsal-fin base twice as wide as interspace (vs. bars narrower than interspace); head coloration plain (vs. vermiculated pattern); pectoral-fin rays, pelvic-fin rays, and anal-fin rays hyaline (vs. black); and head length greater (dorsally: 22.4–28.7% vs. 18.5–21.0%).

Schistura falamensis sp. nov. can be distinguished from S. yingjiangensis by dorsal-fin origin in middle of body (vs. anterior of midpoint of body); 5–8 bars on body (vs. 18–22); basal caudal bar disassociated (vs. complete and round); and 1 row of black spots on caudal fin (vs. 2).

Thirteen species of Schistura have been described from two major drainages of Manipur, viz., S. kangjupkhulensis (Hora 1921) , S. khugae Vishwanath & Shanta 2004 , S. nagaensis (Menon 1987) , S. manipurensis (Chaudhuri 1912) , S. prashadi (Hora 1921) , S. reticulata Vishwanath & Nebeshwar 2004 , and S. phamhringi (Lokeshwor & Vishwanath 2014) from the Chindwin drainages, and S. chindwinica (Tilak & Hussain 1990) , S. fasciata Lokeshwor & Vishwanath 2011 , S. minuta Vishwanath & Shantakumar 2006 , S. tigrina Vishwanath & Nebeshwar 2005 , S. ferruginea (Lokeshwor & Vishwanath 2013) , and S. liyaiensis (Lokeshwor & Vishwanath 2014) from the Barak drainages. Schistura falamensis sp. nov. can be readily distinguished from S. kangjupkhulensis , S. khugae , S. nagaensis , S. manipurensis , S. fasciata , S. minuta , S. tigrina , S. ferruginea , and S. liyaiensis by lateral line complete (vs. incomplete).

Schistura falamensis sp. nov. can be distinguished from S. phamhringi by black basicaudal bar disassociated (vs. arc-shaped); caudal fin deeply forked (vs. deeply emarginated); 3 black spots at base of dorsal fin (vs. 1); semicircular suborbital flap (vs. prominent oar-like); processus dentiformis weak (vs. prominent and broad); and 9 pectoral fin rays (vs. 12).

Schistura falamensis sp. nov. can be distinguished from S. reticulata by 5–8 bars on body (vs. 17–29); 17 (9+8) branched caudal fin rays (vs. 15); basicaudal bar disassociated (vs. complete); and, head length longer (dorsally: 22.4–28.7% SL vs. 19.3–21.0%; laterally: 23.0–28.0% SL vs. 20.3–22.4%).

Schistura falamensis sp. nov. can be distinguished from S. chindwinica by bars behind dorsal-fin base twice as wide as interspace (vs. narrower than interspace); low adipose crest present (vs. absent); bulge present dorsally at base of pectoral fin (vs. absent); caudal fin deeply forked (vs. deeply emarginated); 3 black spots at base of dorsal fin (vs. 1); spots at pelvic fin absent (vs. 2 rows of black spots); upper lip with incision present (vs. absent); head length longer (dorsally: 22.4–28.7% SL vs. 18.5–20.8%).

Figures

FIGURE 1. Schistura falamensis sp. nov., KIZ 2018002396, holotype, 35.9 mm SL; Myanmar: Irrawaddy River drainage: Manipur River near Falam District.

FIGURE 2. Schistura falamensis sp. nov., KIZ 2018002396, holotype, 35.9 mm SL; mouth.

FIGURE 3. Schistura falamensis sp. nov., SEABRI S20181108, paratype, 37.1 mm SL; digestive tract. Scale bar = 1 mm.

FIGURE 4. Schistura falamensis sp. nov., KIZ 2018002396, holotype; male, 35.9 mm SL, with suborbital flap.

FIGURE 5. Schistura falamensis sp. nov., SEABRI 20191137, paratype; female, 24.7 mm SL, with suborbital groove.

FIGURE 6. Schistura falamensis sp. nov., KIZ 20018002396–2399, SEABRI 20181108, 20191137, paratypes: a, 24.7 mm SL; b, 26.1 mm SL; c, 31.2 mm SL; d, 36.7 mm SL. Scale bar = 5 mm.

FIGURE 7. Schistura falamensis sp. nov., SEABRI 201902692, paratype, 37.3 mm SL; shortly after capture, Myanmar: Irrawaddy River drainage: Manipur River near Falam District.

FIGURE 8. Type localities of Schistura falamensis sp. nov. and Schistura altuscauda sp. nov., solid line indicates international boundaries.

FIGURE 9. Manipur River, type locality of Schistura falamensis sp. nov..