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Echinoderms
Echinoderm (Echinodermata) means spiny- skinned. Echinoderms include many ancient forms of life that have survived to the present day, such as crinoids and sea urchins (echinoids).
Crinoids
Crinoids, which are animals although they are often called sea lilies, are among the oldest echinoderms. The main body, or calyx, is supported on a stem made of many ossicles. In many cases, the bottom of the stem is anchored to the sea bed.
Crinoids, like other echinoids, are
noted for their five-fold symmetry. Five arms are attached to the cap, again made of ossicles. The arms are covered in tiny hairs (called cilia) that
(Below) Ossicles from the stem of a crinoid.
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(Below) Crinoid stems, calyx and arms preserved in a Silurian ironstone.
