This study presents a description of the life histories of all four species of the genus Phallichthys, found primarily in the Atlantic slope of Central America (ranging from northern Panama to Mexico), based on a combination of data collected from preserved and living specimens. All species produced a single litter of offspring before developing another brood (i.e. no superfoetation). In the laboratory, the mean time interval between successive litters ranged from 24 to 48 days, further suggesting that they lack superfoetation. Embryos lose from 15 to 65% of their dry mass during development, meaning all or the large majority of resources required for development are provided prior to fertilization (lecithotrophy). All mature male size distributions were platykurtotic and appeared either bimodal or multimodal. Multimodal and skewed size distributions have been associated with genetic polymorphisms for size at maturity in other species of Poeciliidae. As the sister clade to Phallichthys includes genera in which all species have superfoetation (Neoheterandria and Poeciliopsis), these results suggest that their common ancestor with Phallichthys also had superfoetation and that the trait has been lost.