Phocidae (family)

Family containing 19 species in ten genera, characterized as being highly specialized for aquatic life, returning to dry land or pack ice to breed and give birth, lacking external ears, having sleek streamlined bodies, nipples that can be retracted, internal testicles, a penis in an internal sheath, a layer of blubber under the skin, the ability to divert blood to the blubber level to help control their temperature, fore-flippers that are used primarily for steering, and hind flippers bound to the pelvis in such a way that they cannot be moved under the body for walking.