Echinoderm Evolution
The echinoderms are a phylum of invertebrate animals that includes starfish, sea urchins, and sand dollars. One feature that distinguishes echinoderms from other groups of organisms is their system of locomotion-the bottoms of echinoderms are covered with a number of tiny tube feet, which aid the echinoderm in feeding and slow movement on the ocean floor Like other invertebrates, echinoderms lack a backbone and have a fairly primitive nervous system. Unlike many invertebrates, the soft bodies of which are often poorly preserved as fossils, echinoderms have hard internal skeletons made of calcite. For this reason, echinoderms are well represented in the fossil record. In spite of their generally good preservation as fossils, there are several puzzles surrounding the evolution of echinoderms.
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