Abstract
Botia eos is described as a new species from the Menam Chao Phya and the Mekong drainages in Thai-Lao region.The new species is distinguished from other related species primarily by having 10-41 branched dorsal rays.Its closest relatives appear to be B. horae and B.lecontei.The holotype and other specimens of B.lecontei are also described to supplement the original description. The genus Botia is usually divided into three subgenera, i.e., Botia, Hymenophysa, and Sinibotia.In Hymenophysa, which is represented by a Burmese and all Thai-Lao species except B.helodes, two distinct species-groups are recognized: one, hymenophysa-group, is charac-terized chiefly by the premaxillae with sickle-shaped anterior projections surrounding a cavity between them and small, simple mental lobes on the lower lip, and the other, modesta-group, to which B.eos is to be referred, by the ordinary premaxillae not surrounding a cavity and relatively large mental lobes with a pair of small fleshy papillae on each the lobe.The two species-groups, however, agree with each other in having a large fontanelle on the top of cranium, a less developed osseous capsule of gas-bladder, and a large posterior chamber of gas-bladder.B.macracantha is generally regarded as belonging to the subgenus Botia together with all Indian forms.However, though it approaches the subgenus Botia in the feature of the mental lobe, it shares the characters of the fontanelle and the gas-bladder with Hymenophysa rather than Botia.The morphological distinctness of B.macracantha and its range far apart from the main habitat of the subgenus Botia in India may probably suggest its unique phylogenetic position.
