Sea jellies, sometimes called jellyfish, are boneless, brainless and heartless,
and are made almost entirely of water. They are also survivors, and have
been around since before the dinosaurs.

Size  Up to 15 inches in diameter

Diet  Plankton, including small shrimps, fish eggs and larvae

Lifespan  Adults live 3-6 months; polyps can live several years.

Range  Temperate and tropical oceans and bays worldwide

Habitat  Most common in bays or harbors, but can live in many habitats

Predators  Sea turtles, some fishes and other types of sea jellies

Relatives  There are more than 2,000 species of sea jellies in the world.
Sea jellies are also related to anemones and coral.

Family life  Sea jelly eggs are fertilized when the female ingests floating strands of sperm that were released by an adult male. When the female releases her fertilized eggs, they develop into a larval form known as a planula. The planula floats in the water until it finds a hard surface, where it anchors itself and morphs into a polyp. The polyp looks like an anemone or an upside-down sea jelly. When conditions are right, the polyp divides itself into a stacked series of saucer-like clones that then break off and swim away. Known as ephyra, these are basically very small sea jellies. As the ephyra grow larger, they mature into adult sea jellies.

Conservation status  Stable  Moon jellies are survivors. In fact, scientists have discovered that many sea jellies thrive in dirty, polluted and oxygen-poor water.

Explore other profiles   Check out Atlantic harbor seals, giant Pacific octopus and American lobsters.