Macrognathus orthosemos, a new species of spiny eel from southern Myanmar (Teleostei: Synbranchiformes: Mastacembelidae)

Macrognathus orthosemos, a new species of the M. aculeatus group, is described from the Tanintharyi Region in Myanmar. It is distinguished from the other species of this group by the following combination of characters: 9-11 rostral tooth plates, 17-19 dorsal-fin spines, 50-57 dorsal-fin rays, 50-54 anal-fin rays, 75-78 vertebrae, and a colour pattern consisting of a series of parallel oblique bars on the side of the body, combined with 8-12 ocelli along the dorsal-fin base and 7-9 dark spots along the anal-fin base.