Stone skeletons
When you were born, your skeleton was already inside you. However, there
are creatures in the sea that are born without skeletons—so they make
their own. But their skeletons are on the outside!
Many kinds of these creatures live in large groups. Their skeletons, all
fastened together, form big, stone \”apartment buildings” beneath the
waves! These clumps of stone are called coral [(kawr]{.smallcaps} uhl).
They may look like wrinkled balls, heads of lettuce, or clusters of
small, stubby tree branches. Some of them make up underwater formations
known as coral reefs. The little creatures that live in them are coral
animals, or polyps [(pahl]{.smallcaps} ihps).
A coral polyp has a body like a sack, with a row of tentacles around the
top. The opening in the sack is the coral polyp’s mouth. A polyp uses
its tentacles to catch food and to push the food into its mouth.
A coral polyp makes its skeleton out of chemicals that it takes from the
water. This skeleton, a hard material called limestone, is like a cup.
During the day, the polyp hides in the bottom of the cup. At night, the
polyp stretches its sacklike body upward and puts out its tentacles to
catch food. It eats tiny plankton creatures.
When all the polyps in a piece of coral are hiding, the coral looks like
stone. But when the polyps put their tentacles out, the coral looks like
a fantastic flower garden. The \”flowers” are really the beautifully
colored tentacles of the polyps.
Not all coral is made up of stony, outside
soft coral
sea tan coral
skeletons that look like rock. Two kinds of coral have inside skeletons.
These corals don’t look at all rocklike. One kind may take the shape of
a fan or a feathery plume. The other kind, called soft coral, often
looks like a little tree or like the antlers of a deer. And one kind of
soft coral even looks like a lumpy human hand. This lumpy coral is
called dead men’s fingers.
