Super Order: Batoidea
No swim bladders, maintaining buoyancy instead with large livers that are full of oil e.g. squalene. This stored oil may also function as a nutrient when food is scarce.
Five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper.