Considered a synonym of Poecilia petenensis (Günther, 1866)
- Rosen, Donn E & R.M. Bailey. 1963. "The poeciliid fishes (Cyprinodontiformes), their structure, zoogeography, and systematics". Bulletin of the American Museum of Natural History. 126(1):1-176 (ffm04566)
Original description as Mollienesia gracilis:
- Regan, Charles Tate. 1913. "A revision of the cyprinodont fishes of the subfamily Poeciliinae". Proceedings of the Zoological Society of London. 1913:977-1018 (ffm00016)