JELLYFISH. Among the most unusual of sea animals are the jellyfishes.
Cousins of the jellyfishes are the corals and sea anemones. These three
belong to the phylum of animals known as Coelenterata.
The jellyfish has none of the characteristics of fishes.
It has no skeleton, and more than nine tenths of its body
is jellylike. In some forms not much more than 1 percent
is living matter. There are about 200 known species, varying in form,
size, and color. A typical jellyfish may be umbrella-shaped, with few
or many feelers, or tentacles. Sometimes it has simple eyes around the
edge of the umbrella. The mouth and stomach are in the "handle" of the
umbrella. Simple muscles on the underside contract the body much like
the closing of an umbrella and enable the jellyfish to swim. The
tentacles have stinging cells that produce poisons that paralyze other
small animals. Then the tentacles draw them into the mouth of the
jellyfish. A network of nerves runs beneath the lining of the
umbrella and coordinates the muscles.

During most of their lives, the larger jellyfishes swim about freely.
Many reproduce by the process shown in this article. Some smaller
jellyfish spend most of their lives as attached polyps. A new individual
develops from a fertilized egg and swims about for a short time. Then it
attaches itself to rocks or seaweeds and develops an internal cavity,
a mouth, and tentacles. From each polyp others develop as buds. Some of
them remain attached to the parent and form a colony
Others break away and become jellyfish. The budding process, following
reproduction by fertilized eggs, is called alternation of generations.

Some jellyfishes are scarcely large enough to be seen.
Others are 2 feet (0.6 meter) or more in diameter. Some are delicate.
Others are almost as firm as gristle. Jellyfish may be transparent or
brown, pink, white, or blue. Some are egg-shaped or ribbonlike. Others,
such as the Portuguese man-of-war, are more complex. Most jellyfishes
live at or near the surface of the sea, though a few live at the bottom.
Some are phosphorescent, glowing eerily in the sea.