Astergnathidae

Astergnathidae is a family of Astergnathiformes distinguished by the lack of vertebrae in front of the pelvic ring. They typically have a membrane between their anal fingers which can be pulled back for mating, and their lateral arms are modified to be flipper-like.

All Astergnathid species have a pelvic ring and vertebrae. They swim with horizontal tail fins, like a Terran dolphin, and they have four sets of gills. While having pinhole eyes is the ancestral state, most species have since evolved camera eyes of varying complexity.