the same clade within that genus. However, their modes of maternal provisioning vary greatly. P. monacha can be considered to be lecithotrophic because it does not really provide any resources for its offspring after fertilization - the pregnant female is basically a swimming egg sac. P. lucida shows an intermediate level of matrotrophy, meaning that to a certain extent the offspring's metabolism can actually affect the mother's metabolism, allowing for increased nutrient exchange. P. prolifica is considered to be highly matrotrophic, and almost all of the nutrients and materials needed for fetal development are supplied to the oocyte after it has been fertilized. This level of matrotrophy allows Poeciliopsis to carry several broods at different stages of development, a phenomenon known as superfetation. Because the space for developing embryos is limited, viviparity reduces brood size. Superfetation can compensate for this loss by keeping embryos at various stages and sizes during development. P. elongata, P. turneri, and P. presidionis form another clade that could be considered an outgroup to the P. monacha, P.lucida, and P. prolifica clade. These three species are very highly matrotrophic - so much so that in 1947, C. L. Turner described the follicular cells of P. turneri as "pseudo-placenta, pseudo-chorion, and pseudo-allantois". The greater degree of matrotrophy in a species is linked with a higher degree of placentation, including "a thicker maternal follicle, higher degree of vascularization, and greater number of villi in the placenta". The reason for placental evolution in Poeciliids is controversial, and involves two major groups of hypotheses, adaptive and conflict hypotheses. Adaptive hypotheses, including the locomotor hypothesis, Trexler-DeAngelis Model (reproductive allotment), and life-history facilitation, broadly suggest that the placenta evolved to facilitate the evolution of another advantageous trait in the fish’s environment. The conflict hypothesis suggests the placenta is a nonadaptive byproduct of genetic "tug-o-war" between the mother and the offspring for resources. Subfamilies and tribes The family is divided into subfamilies and tribes as follows: Subfamily Aplocheilichythinae Myers, 1928 (Banded lampeyes) Genus Aplocheilichthys Bleeker, 1863 Genus Hylopanchax Poll & J. G. Lambert,1958 Subfamily Procatopodinae Fowler, 1916 (Lampeyes) Tribe Fluviphylacini Roberts, 1970 Genus Fluviphylax Whitley, 1920 Tribe Procatopodini Fowler, 1916 Genus Laciris Huber, 1981 Genus Micropanchax Myers, 1924 Genus Lacustricola Myers, 1924 Genus Poropanchax Clausen, 1967 Genus Platypanchax Ahl, 1928 Genus Lamprichthys Regan 1911 Genus Pantanodon Myers, 1955 Genus Hypsopanchax Myers, 1924 Genus Procatopus Boulenger, 1904 Genus Plataplochilus Ahl, 1928 Genus Rhexipanchax Huber,