Nemacheilus zonatus, Page & Pfeiffer & Suksri & Randall & Boyd, 2020

Page, Lawrence M., Pfeiffer, John M., Suksri, Siriwan, Randall, Zachary S. & Boyd, David A., 2020, Variation in the Arrow Loach, Nemacheilus masyae (Cypriniformes: Nemacheilidae), in Mainland Southeast Asia with Description of a New Species, Copeia 108 (2), pp. 392-402 : 393-398

Nemacheilus zonatus , new species urn:lsid:zoobank.org:act:4981B890-66D2-4034-A83E-3B6C42E33F8A

Banded Arrow Loach

Figures 3–5 , Tables 1–2

Holotype.— NIFI 5114 , 24.1 mm SL, Thailand, Kalasin Province, Mekong River basin, Mun River drainage, Pao River (tributary of Chi River ), at route 214 bridge, Kamalasai District , 16.340228N, 103.575848E, L. M. Page, Z. S. Randall, J. M. Pfeiffer, and D. A. Boyd, 6 January 2015.

Paratypes.— All Thailand, Mekong River basin. UF 237302 , 5 , 23.2–28.6 mm SL, same data as holotype; ZRC 61125 , 1 , 23.2

mm SL, same data as holotype. Mun drainage: UF 170212 , 1 , 22.6 mm SL, Ubon Ratchathani Province, Mun River at Warinchumraj , 15.178628N, 104.706658E, W. Tangjitjaroen, J. Grudpan, S. Udduang, and L. M. Page, 16 November 2007 ; UF 237301 , 4 , 15.3–18.3 mm SL, Surin Province, Mun River, Tha Tum District , 15.315348N, 103.629858E, J. M. Pfeiffer, L. M. Page, D. A. Boyd, and Z. S. Randall, 6 January 2015 . Songkhram drainage: UF 188240 , 3 , 20.0– 25.2 mm SL, Sakon Nakhon Province, Songkhram River at bridge west of Ban Na Si Nuan on route 2281, Charoen Sin District , 17.729478N, 103.410738E, Z. S. Randall, J. M. Pfeiffer, M. Tan, D. A. Boyd, N. Warin, and R. Itimung, 25 January 2016 ; UF 188447 , 3 , 20.9– 24.4 mm SL, Sakon Nakhon Province, Un River (tributary of Songkhram River), at route 222 bridge, Phang Khon District , 17.442638N, 103.727638E, D. A. Boyd, Z. S. Randall, J. M. Pfeiffer, R. Itimung, N. Warin, and M. Tan, 25 January 2016 .

Diagnosis.— Nemacheilus zonatus is distinguished from all other species of Nemacheilus in southeast Asia by the presence of 8–12 thin dusky black bars along the side of the body that cross over the back and join the bars on the other side and the small body size—to 29 mm SL.

Molecular data indicate that N. zonatus is most closely related to N. masyae ( Fig. 2 ), which reaches a much larger size (to 66 mm SL), has black blotches rather than uniformly thin bars along the side of the body, black saddles along the dorsal midline, and a conspicuous black spot on the anterior dorsalfin rays. Nemacheilus zonatus also has a shorter snout (24–32 vs. 35–44% HL), a smaller gape (12–18 vs. 17–26% HL), an ethmoid complex that is broad with large anterolateral flanges and narrowest at its middle then widening to its contact with the frontal (vs. ethmoid complex narrow with small anterolateral flanges, narrowest anteriorly then widening slightly to its contact with frontal; Fig. 4 ), and 34 total vertebrae (n ¼ 2 specimens) vs. 36 in N. masyae (n ¼ 1).

The other ten species of Nemacheilus known from mainland southeast Asia, N. arenicolus , N. banar , N. binotatus , N. cleopatra , N. longistriatus , N. ornatus , N. paucimaculatus , N. platiceps , N. selangoricus , and N. troglocataractus , are larger, at least 40 mm SL, and except for N. troglocataractus , which is a cave-inhabiting species that lacks dark pigment, have much more dark brown or black pigment on the back and side of the body ( Kottelat, 1990, 1998; Freyhof and Serov, 2001; Bohlen and Šlechtová, 2011). Nemacheilus arenicolus has 8–13 large brown blotches along the side and 7–11 brown blotches along the back, N. banar has 8–13 dark blotches along the side and 9–15 dark blotches along the back, N. binotatus has a black stripe along the side of the body and a black stripe along the back, N. cleopatra has 9–13 vertically elongated dark blotches along the side and 8–11 dark blotches along the back, N. longistriatus has 8–12 dark brown to black blotches along the side overlain with a black stripe and 9–14 dark brown blotches along the back, N. ornatus has 8–17 black blotches along the side and irregular black blotches along the back, N. paucimaculatus has 8–12 wide dark brown bars along the side and 8–10 dark brown blotches along the back, N. platiceps has 14–16 irregular brown bars, usually split ventrally, on the side that cross over the back and join the bars on the other side, and N. selangoricus has 8–12 dark brown bars much wider than the interspaces along the side of the body that cross over the back and join the bars on the other side. Nemacheilus longipectoralis , restricted to Borneo, is similar to N. zonatus in that it has dark bars on the side of the body that cross over the back (see Hadiaty and Kottelat, 2010: fig. 8), but the bars are wider—as wide or wider than interspaces—and more numerous (16–20 vs. 8–12 in N. zonatus ).

Description.— Morphometric data in Table 2; meristic data in Table 3. Nemacheilus zonatus has slender, slightly compressed body; slenderest at caudal peduncle, deepest at nape. Snout pointed; mouth slightly subterminal, slightly arched; lips thin; upper lip with shallow furrows, no median notch; lower lip with slightly deeper furrows, shallow median indentation. Anterior nostril a short tube. Processus dentiformis (a bony projection at the symphysis of the upper jaw) present. Three pairs of barbels; maxillary barbel reaches slightly past posterior margin of eye, inner rostral barbel reaches almost to anterior margin of eye; outer rostral barbel reaches to posterior margin of eye. Eye slightly elliptical horizontally =, dorsolaterally positioned, about equal to snout length, to 1 3 head length. Pectoral fin somewhat falcate, with fimbriate distal margin; inner rays short, outermost 2 nd to 4 th rays longest ( Fig. 5A ). In juveniles and females, pectoral fin reaches about half-way from origin of pectoral fin to origin of pelvic fin; in large males, it reaches to pelvic fin. Pelvic fin originates under 4 th to 5 th dorsal ray, reaches slightly past dorsal fin insertion, does not reach anus. Anus about length of eye in front of anal fin. Distal margin of dorsal fin straight, of anal fin convex. Caudal fin deeply forked with upper lobe longer than lower lobe. Small axillary pelvic = lobe. = Suborbital flap on male ( Fig. 5B ). Branched dorsal rays 91 2 – 101 2, = pectoral rays 10–12, pelvic rays 8, branched anal rays 51 2, upper caudal lobe 9 rays, lower caudal lobe 8 rays. Body covered with embedded scales. Lateral line complete. Supraorbital pores 6, infraorbital pores 4 þ 10, preoperculomandibular pores 9, supratemporal pores 3. Vertebrae (2 specimens): 34 (22 abdominal including Weberian complex þ 12 caudal). In dorsal view, ethmoid complex broad with long, broad anterolateral flanges, ethmoid narrowest at middle then widening steeply to its contact with frontal ( Fig. 4A ).

Color in life.— Body nearly translucent with light yellow back and upper side; 8–12 thin, dusky bars on side of body and over back. Bars much thinner than interspaces. Black bar on nape at posterior margin of head, another bar between eyes, interrupted bar immediately behind nostrils, dusky black patch on side of snout. Bright yellow sheen on cheek, opercle, and anterior part of lateral line. Posterior end of caudal peduncle white with bold, black, somewhat triangular spot. Bright red spot about half-way up most anterior ray of dorsal fin; melanophores in 2 faint bands across fin. Other fins mostly clear; scattered melanophores on leading edge of pectoral fin and proximal portion of anal fin. Caudal fin with scattered melanophores on proximal half, pale white on upper and lower lobes.

Sexual dimorphism.— All specimens were collected in November and January, and sexual dimorphism, if present, may not have been well developed during this period. The largest male, 28.6 mm SL and collected on 6 January 2015, has a well-developed suborbital flap indicating that it was an adult. A smaller male, 27.0 mm SL, from the same collection has a developing flap ( Fig. 5B ). About half of the specimens, including the two males with a suborbital flap, had tubercles along the rays on the lower surface of the pectoral fin.

Etymology.— The epithet zonatus is a Latin adjective meaning ‘‘banded’’ or ‘‘barred’’ in reference to the bars along the side of the body that cross over the back and meet the bars on the opposite side.

Distribution and habitat.— Nemacheilus zonatus is known from the Mun and Songkhram river drainages ( Fig. 6 ) on the Korat Plateau of Thailand. These large drainages have expansive areas of sandy substrate where this species is found in moderate flow near the banks.

Figures

FIG. 3. Lateral view of NemacheiluS zonatuS, paratype, UF 188240, 25.2 mm SL.

FIG. 4. Lateral and dorsal CT scans of: (A) NemacheiluS zonatuS, UF 237302, lateral view, 23.2 mm SL, UF 237302 (2nd specimen), dorsal view, 27.0 mm SL; (B) N. maSYae, UF 188670, lateral and dorsal views, 38.5 mm SL. Dorsal surface of ethmoid complex highlighted.

FIG. 5. NemacheiluS zonatus: (A) pectoral fin, UF 188447, 24.4 mm SL; (B) suborbital flap, UF 237302, 28.6 mm SL.

FIG. 2. Combined (CO1þRAG1) maximum likelihood phylogenetic reconstruction of (A) NemacheiluS with N. maSYae clade collapsed and (B) N. maSYae complex. Samples labeled N. palliduS are those from within the range described by Kottelat (1990) for N. palliduS, including from the type locality (UF 188670). ML ultrafast bootstraps and BI posterior probabilities values are plotted on the branches. See Data Accessibility for tree files.

FIG. 6. Distribution of NemacheiluS zonatuS. Star indicates type locality. Dashed red line outlines Khorat Plateau ecoregion (Abell et al., 2008).