Department of Zoology, Lady Keane College, Shillong, India.
Department of Zoology, Gauhati University, Guwahati, India.
J Fish Biol. 2024 Oct;105(4):1240-1255. doi: 10.1111/jfb.15856. Epub 2024 Jul 31.
A new species of nemacheilid loach, Schistura sonarengaensis sp. nov., is described from three cave-dwelling populations (Barak-Surma-Meghna drainage) in the South Garo Hills district of Meghalaya, India. The new species possesses prominent eyes but is easily distinguished from all the congeners of the genus Schistura from Barak-Surma-Meghna and adjacent rivers drainages of northeast Indian (except S. syngkai) in having 13-26 vertically elongated to circular mid-lateral black blotches (brownish in life) overlayered on a grayish-black mid-lateral stripe on a dull white or pale-beige (golden brown in life) body. However, it can be easily distinguished from S. syngkai in having a complete (vs. incomplete) lateral line with more 72-89 (vs. 19-42) lateral-line pored scales, greater pre-dorsal length (48.5-53.1 vs. 41.9-44.1 %SL), a wider body at dorsal-fin origin (11.3-16.7 vs. 9.4-10.3 %SL), greater dorsal (18.1-21.1 vs. 15.1-17.0 %SL) and lateral (20.9-24.1 vs. 17.4-18.9 %SL) head length, a wider head (14.5-18.5 vs. 11.6-13.3 %SL), and moderately forked (vs. emarginated) caudal fin. Further, molecular analysis confirms the distinctiveness of S. sonarengaensis sp. nov. from its congeners found in northeast India by significant divergences with uncorrected genetic distance ranging from 3.7% to 17.3% in the mitochondrial cytochrome c oxidase subunit I (COI) gene dataset. The phylogenetic position of the new species with its sister species was evaluated using maximum likelihood and Bayesian analysis. The species delimitation approaches assemble species by automatic partitioning (ASAP) and Poisson tree processes (PTP) utilized for testing species assignments consistently identified our test group as a distinct species from its sister species. Although the new species lacks typical morphological adaptations usually associated with a subterranean life, such as complete absence (or vestigial presence) of eyes and pigmentation, it exhibits a reduction of pigmentation when compared to the epigean congeners.
一种新的泥鳅科泥鳅属鱼类，即新种索兰加恩氏泥鳅（Schistura sonarengaensis sp. nov.），描述自印度梅加拉亚邦南加罗丘陵区三个洞穴（巴拉克-苏里马-梅格纳水系）的洞穴种群。新种具有显著的眼睛，但与巴拉克-苏里马-梅格纳及其相邻河流的泥鳅属的所有近缘种（除了 S. syngkai）明显不同，具有 13-26 个垂直拉长至圆形的侧线黑色斑纹（生活中呈棕色），覆盖在灰色-黑色的侧线条纹上，身体呈暗淡的白色或浅米色（生活中呈金棕色）。然而，它与 S. syngkai 很容易区分，因为它具有完整的（而不是不完整的）侧线，具有更多的 72-89 个（而不是 19-42 个）侧线孔鳞片，更大的前背长（48.5-53.1 比 41.9-44.1%SL），在背鳍起点处更宽的身体（11.3-16.7 比 9.4-10.3%SL），更大的背鳍（18.1-21.1 比 15.1-17.0%SL）和侧线（20.9-24.1 比 17.4-18.9%SL）头长，更宽的头部（14.5-18.5 比 11.6-13.3%SL）和适度分叉的（而不是凹入的）尾鳍。此外，分子分析证实了新种 S. sonarengaensis sp. nov. 与其在印度东北部发现的近缘种的独特性，通过线粒体细胞色素 c 氧化酶亚基 I（COI）基因数据集的未校正遗传距离从 3.7%到 17.3%的显著差异得到证实。利用最大似然法和贝叶斯分析评估了新种与其姐妹种的系统发育位置。物种划分方法通过自动分区（ASAP）和泊松树过程（PTP）进行物种组合，用于测试物种分配的方法一致地将我们的测试组识别为与其姐妹种不同的独特物种。尽管新种缺乏通常与地下生活相关的典型形态适应，例如完全缺乏（或退化存在）眼睛和色素，但与表生近缘种相比，它的色素沉着减少。
