Cyprinodontiformes: Monophyly of this order is recognized on the basis of several derived characters: e.g., caudal fin symmetrical, supported internally by one epural; first pleural rib on second vertebrae rather than third; primitively, low-set pectoral girdle with a scalelike postcleithrum; an alveolar arm of the premaxillae; extended developmental period. In addition, they possess the following characters: lateral line canal and pores chiefly on head, lateral line represented on body only by pitted scales; narial opening paired; branchiostegal rays 3-7; pelvic fins and girdle present or absent; upper jaw bordered by premaxilla only, protrusible; vomer usually present and supracleithrum always present; metapterygoid usually absent and ectopterygoid always absent; parietals present or absent; vertebrae 24-54. Marked sexual dimorphism with the males often brightly colored.
- See Fishbase.
Families in this order: