Background: The Cynopoecilus melanotaenia complex is a morphologically homogeneous killifish group, endemic from an area encompassing southern Brazil and northeastern Uruguay. It presently comprises four valid species: C. melanotaenia, the type species of the genus, and C. fulgens, C. intimus, and C. nigrovittatus.
New information: Cynopoecilus feltrini, n. sp., from the lower Tubarão river basin, southern Brazil, is distinguished from all congeners of the C. melanotaenia complex by having frontal E-scales medially overlapped, branchiostegal region orangish red in males and dorsum with few dark brown spots above opercular region. A phylogenetic tree derived from the analysis of a fragment of the mitochondrial gene cytochrome c oxidase subunit I (681 bp) indicates that C. feltrini is a member of the clade that includes all species of the C. melanotaenia complex except C. melanotaenia, as well as that C. feltrini is the sister group of a clade comprising C. fulgens and C. nigrovittatus.
Keywords: Aplocheiloid killifishes; Internal fertilization; Molecular phylogeny; Neotropical region; Systematics.