The Vaquita is a cetacean

Cetaceans are a subgroup of mammals, mostly marine, distinguished among other things, for living their entire life in water. Adaptations for a totally aquatic life include changes in external body form to subtle physiological changes that allow for life in salt water.

All cetaceans are large animals, which enables them to maintain body heat. They have a hydrodynamic, torpedo shape, almost without protuberances, which allows them to slide smoothly through the water. For example, they do not have external ears, the reproductive organs are internal, they have no hind legs, and they have almost no hair, except for some minute sensory hairs on the snouts of some whales. The skeleton is adapted to this cylindrical shape, and the anterior extremities are fins. The main propulsive force is the flukes. Most cetaceans have a rigid dorsal fin that provides stability and helps disperse body heat.

Cetaceans have an elongated head with the breathing orifices in a dorsal position, and they have a subcutaneous layer of fat that can measure tens of centimeters thick in some species of whales.

Internal adaptations of cetaceans include a stomach with various compartments and adaptations of the circulatory system for diving and regulation of internal body temperature.