Sponges, sea squirts, and worms

sponges

An animal that never moves

Sitting on the sea bottom is an object that looks like a black, lumpy
ball. It never moves. It cannot see, hear, or smell. It has no head or
mouth, no nerves, muscles, heart, or stomach. Yet, it is an animal—the
animal called a sponge.

You may have thought a sponge was a piece of rough, colored plastic used
for washing things. But these are man-made sponges, named after the sea
animal. You see, for thousands of years, people used the skeletons of
real sponges for washing things. The skeletons are soft and hold lots of
water. People called them sponges, after the animals that once lived in
them. When pieces of colorful plastic came into use, people called them
sponges, too.

A sponge has no tentacles for catching food. It doesn’t even have a
mouth for eating. It simply strains its food out of the water. A
sponge’s body is filled with many tiny holes, so water goes right
through it. Tiny plants and animals in the water are trapped inside the
sponge and digested.

There are about five thousand different kinds of sponges. Some are like
lumpy balls. Some are clusters of fat tubes. Some look like big vases or
bowls.

Some sponges begin life as tiny eggs in a grown-up sponge’s body. The
eggs are carried outside by the water that goes through the grown-up.
But sponges also grow little \”buds” that break off and become new,
small sponges.