Poecilia obscura is a small poeciliid species from the subgenus Acanthophacelus (SL in males usually not exceeding 20 mm and in females 30 mm), which is distinguished

from all other species of the subgenus by the following characters: comb-like spines of gonopodium ray 3 not numerous (11 to 15), basal massive, vs. numerous (14 to 18), basal slender in P. reticulata and P. wingei. Being genetically divergent from the other species of the subgenus, the definition of the new species is mainly based on evidence from DNA sequence (Ref. 82825).