|[upper] Nemacheilus zonatus ปลาค้อ|
Page, Pfeiffer, Suksri, Randall & Boyd, 2020
[A, B, C] Nemacheilus masyae H. M. Smith, 1933
Analyses of morphological and molecular data from recently collected specimens of Nemacheilus from Cambodia, Malaysia, and Thailand indicate that N. pallidus is a junior synonym of N. masyae, and an undescribed species of Nemacheilus occurs in large tributaries of the Mekong River in Thailand. The new species, described herein, is small—with a maximum-known standard length of 28.6 mm—and has a distinctive color pattern of dusky black bars along the side of the body that cross over the back and join the bars on the other side. Molecular phylogenetic analyses suggest that the new species is most closely related to N. masyae, which reaches a much larger size—to 66.2 mm SL—and otherwise is easily distinguished from the new species. The new species is known from the Songkhram and Mun river drainages in Thailand and appears to be restricted to the Khorat Plateau ecoregion of the Mekong River basin. Nemacheilus masyae occurs throughout mainland southeast Asia, including in the Chao Phraya, Mae Klong, Mekong, and coastal drainages of the Malay Peninsula.
|Lateral view of Nemacheilus zonatus, paratype, UF 188240, 25.2 mm SL. |
Lateral and dorsal CT scans of Nemacheilus zonatus, UF 237302, lateral view, 23.2 mm SL.
Nemacheilus zonatus, new species
Banded Arrow Loach
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 dorsal-fin 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 = 2 specimens) vs. 36 in N. masyae (n = 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).
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.
|Fig. 6 Distribution of Nemacheilus zonatus.|
Star indicates type locality. Dashed red line outlines Khorat Plateau ecoregion (Abell et al., 2008).
Lawrence M. Page, John M. Pfeiffer, Siriwan Suksri, Zachary S. Randall and David A. Boyd. 2020. Variation in the Arrow Loach, Nemacheilus masyae (Cypriniformes: Nemacheilidae), in Mainland Southeast Asia with Description of A New Species. Copeia., 108(2): 392-402. DOI: 10.1643/CI-19-305