Echinoderms are unique with a pentameral symmetry, best shown by the star fish.
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All echinoderms are marine, with a test (shell) made of calcite plates covered by skin.
Regular Echinoids are the “sea urchins” of modern seas (see photograph) with an almost spherical test covered
in spines. They wander across the sea floor obtaining food by scavenging or by grazing on other organisms such
as worms, algae and coral, using a sharp jaw. They move in any direction and so their symmetry is approximately
radial.
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Irregular Echinoids have adapted to a burrowing mode of life. They move in one direction as they burrow - or
face in the direction from which the food arrives - and therefore develop bilateral symmetry.
Geopix Study Guide "Echinoids and Crinoids"
- gives an illustrated description of the echinoderms;
- describes the main morphological features of echinoids and crinoids;
- explains how the mode of life can be determined;
- describes the differences between the regular and irregular echinoids;
- describes and interprets the evolution of the Micraster.
The Study Guide contains the following pages:
'Echinoids and Crinoids' is part of the Geopix Fossils Study Guide CD.
To order this CD go to the Geopix Online Store
