Systematic revision of east African Oligolepis (Oxudercidae: Gobionellinae) reveals a distinct species, Oligolepis goni sp. nov., formerly assigned to Oligolepis acutipennis (Valenciennes, 1837).

Species of the gobionelline genus Oligolepis Bleeker, 1874 (Oxudercidae) are small gobies inhabiting muddy estuaries, coastal bays and lagoons, with some extending into freshwater systems. All recognised species occur in the western Pacific and eastern Indian oceans, except Oligolepis acutipennis (Valenciennes, 1837), previously considered widespread across the Indo-West Pacific to include the western Indian Ocean. Populations from the east African coast have traditionally been assigned to this species. Phylogeographic analysis of mitochondrial COI sequences reveals two deeply divergent lineages within O. acutipennis sensu lato: one distributed from the Indian subcontinent to the western Pacific, and another restricted to east African estuaries from South Africa to Kenya. The lineages differ by 5% sequence divergence and show allopatric distributions, with no confirmed records between Kenya and western India. Males of the Indo-Pacific lineage possess small black spots on the head, jaw membranes and anterior dorsal body, which are absent in the east African lineage. Based on genetic divergence, distributional isolation and several sex-specific differences (most notably the male colour pattern), the east African lineage is described as a new species, Oligolepis goni sp. nov. We further discuss the need for genus revision, considering that species diversity within Oligolepis may be overestimated, with several nominal taxa likely representing conspecific populations of O. acutipennis sensu stricto.