Members of this structurally simple marine group possess one of two body forms. Sea anemones, sea whips, corals and hydroids are polyps growing attached to rocks or other hard surfaces of the sea. Both body forms display radial symmetry with body parts radiating from a central axis. This symmetry allows jellyfish to respond to food or danger from any direction. Four to eight oral arms are located near the mouth and are used to transport food that has been captured by the tentacles.
Jellyfish occur in a wide variety of sizes, shapes and colors.
The tentacles of some jellyfish can reach lengths greater than 100 feet. Jellyfish inhabit every major oceanic area of the world and are capable of withstanding a wide range of temperatures and salinities. The life cycle of a typical jellyfish involves an alteration of generations in which the animal passes through two different body forms. The dominant and conspicuous medusa is the familiar form, while the smaller polyp form is restricted to the larval stage. Jellyfish are either male or female and reproduce sexually.