Description

Each of the various species of sand dollars has a slightly different appearance. They have a somewhat rounded appearance, and many have a flattened body shape. Unlike other sea urchins, they have very short spines with a texture similar to velvet.
These creatures vary greatly in size. Some measure just two or three inches across, while others reach five or six inches across. Most individuals weigh less than an ounce.
Echinoderms are marine invertebrates with a hard, spiny covering or skin and a pentamerous radial symmetry. They include sea lilies, sea urchins, sea cucumbers, starfishes, basket stars, and sea daisies.
The main feature of echinoid fossils is the set of five ambulacra on the test radiating out from a central point, forming a distinctive five-petalled pattern. The earliest echinoid fossils date from the late Ordovician period, some 450 Mya. The group has a rich fossil record, their hard tests made of calcite plates and their spines being found in rocks from every period since then. Echinoids f