The blowhole is opened during their frequent trips to the surface to expel and inhale air. In contrast to some of the large whales, dolphins and porpoises have teeth, which they use to seize their food, consisting primarily of marine fishes and larger invertebrates, such as squid. D olphins and porpoises have two flippers, fins that serve as forelimbs, and an upright triangular fin on the back. Dolphins and porpoises are noted for being graceful swimmers, arcing through long, slow curves that bring the blowhole to the surface of the water and then expose the back fin as the animal dips downward. At first glance, the high dorsal fin somewhat resembles that of a shark and has sometimes caused false alarms at beaches.
Porpoises are somewhat smaller.
Dolphins and porpoises have smooth skin with a rubbery texture. Most species have color patterns that are some combination of black, white, and gray. Like other whales, they have an insulating layer of blubber beneath the skin. M ost dolphins and porpoises have declined in numbers during this century. Some species are hunted commercially, particularly in Asian marine waters.