Mystus impluviatus:: A new species of bagrid catfish (Teleostei: Bagridae) from eastern Borneo

A new species of bagrid catfish in the genus Mystus is described from the Mahakam River drainage in eastern Borneo. Mystus impluviatus closely resembles Mystus nigriceps and Mystus castaneus but differs in having a second posterior fontanel on the supraoccipital. It can be further distinguished from M. nigriceps and M. castaneus a combination of the following characters: maximum height of adipose fin 4.7-6.0% SL, length of adipose fin base 31.6-36. 1% SL, long second and third dorsal fin rays, causing the dorsal fin to appear less rounded, maximum height of pectoral spine serrations 3.6-4.8% of spine length, a deeply forked caudal fin with a slender upper lobe, and a brown body with a distinct dark triangular patch on the base of the caudal peduncle.