Polynemus kapuasensis, a new threadfin (Perciformes: Polynemidae) from western Kalimantan, Indonesia, and a redescription of P. multifilis Temminck & Schlegel, 1843

Polynemus multifilis Temminck & Schlegel, 1843, is redescribed and its synonymy, authorship, type material status and distribution are discussed. In addition, a new species, P. kapuasensis, previously identified as P. multifilis, is described from the Kapuas River, western Kalimantan, Indonesia on the basis of 12 specimens. Polynemus kapuasensis differs from P. multifilis in having higher counts of pectoral filaments (usually 15 on each side of body vs. 14 in the latter), pored lateral line scales [mode 103 (range 100-110) vs. 86 (83- 99)], scale rows above lateral line [10 (9-11) vs. 8 (7 or 8)] and caudal peduncle scales [38 (35-40) vs. 32 (28- 37)], and a shorter pectoral fin [mean 31% (range 29-33%) of standard length], its posterior tip not extending beyond level of anal fin origin in adults [vs. 36% (33-38%), its posterior tip reaching or extending beyond level of anal fin origin throughout life]. The former is currently known only from the Kapuas River system, whereas the latter is known from Thailand (the Chao Phraya River system) and Indonesia (Sumatra and southern Kalimantan). A key to the Polynemus species occurring in Kalimantan is provided.