Abstract: In order to detect taxonomic status of Placocheilu robustus Zhang, He et Chen and P. caudofasciatus (Pellegrin & Chevey) from the Red River system, more reliable taxonomic characteristics are expected to be found from the external morphology and internal skeleton by methods of comparison of the external morphology, anatomic comparison of internal muscle and skeletal. A total of 134 specimens for 2 species would be examined and measured, and three specimens for each species would be dissected. The results showed that there were no differences between two species of Placocheilu in the following characters that their tassel consisted by tubercles in rostral fold not arranged in rows and difficult to count in numbers. The branched ray numbers of dorsal, anal, caudal and ventral fins as well as lateral line scales and scale numbers around caudal peduncle. The predorsal fin scales of P. caudofasciatus could be clearly counted, and that of P. robustus buried in the skin and could not be observed easily. There no obvious difference in the naked and uncovered scales area of thoracic and abdominal between P. caudofasciatus and P. robustus. The ratio of mental adhesive disc length to its width, the disc length to depth of head, depth to length of caudal peduncle were overlapped, and there were no obvious interruption to distinguish the two species of Placocheilu. There were no differences in the mental adhesive disc morphology, head shape, body markings and fin morphology between two species of Placocheilu. The muscle and skeletal morphological comparison results showed that there were no significant differences in muscle and skeletal morphology except slight differences in the composition of the caudal fin base bone. According to the comparison results of external morphology and anatomy, P. robustus could not be differentiated from P. caudofasciatus, and could not be a valid independent species. P. robustus is a synonym of a P. caudofasciatus.

Key words: Placocheilus caudofasciatus, P. robustus, species status, morphology character, taxono- mic character