The moon jelly can reach 16 inches in diameter, and it has four fringed oral arms underneath for food. Moon jellies feed on plankton. It uses its invisibility to conceal itself from predators when there is no place to hide. These jellies have about 200 short tentacles and feed on invertebrates and larvae. Umbrella jellies are known as hydrozoans, which means that their offspring live in colonies as polyps and then bud into small adult-like animals before maturing.
Hydrozoans also tend to be smaller than other species of jellies.
They prefer cool water temperatures and dwell in the North Pacific coast from Santa Barbara, CA to Alaska and the Bering Sea. While only a few of these creatures lack tentacles, all of them are without stinging cells. These creatures have mouths armed with special fangs for trapping prey. Comb jellies get their name from their eight rows of cilia, shaped like the teeth of a comb, which they use for locomotion.