A nyone who has been to the beach has probably seen starfish or
sand dollars. The more intrepid beachcomber may find brittle
stars, sea cucumbers, or sea urchins. These and many other
organisms, living and extinct, make up the Echinodermata, the
largest phylum to lack any freshwater or land representatives.
Most living echinoderms, like this sand dollar from Baja
California, are pentameral; that is, they have fivefold
symmetry, with rays or arms in fives or multiples of five.
However, a number of fossil echinoderms were not pentameral at
all, and some had downright bizarre shapes. Echinoderms have a
system of internal water-filled canals, which in many
echinoderms form suckered "tube feet", with which the animal may
move or grip objects. Click on the buttons below to find out
more about the Echinodermata Visit the Echinoderm Homepage at
the California Academy of Sciences for additional information
and links. Or peruse the Echinoderm Newsletter, brought to you
by the National Museum of Natural History.