Spiny-skinned Invertebrates

The phylum Echinodermata are a group of marine animals that include sea urchins, sea lilies, feather stars, sand dollars, brittle stars, sea daisies, sea cucumbers, and sea stars (starfish). These invertebrates have a water-vascular system that uses seawater to power their tube feet, a skeleton composed of plates of calcium carbonate, and many species have a hard, spiny skin or covering. Extant adult echinoderms have five-part radial symmetry, meaning their bodies are arranged around a central point. Echinoderms can regenerate missing body parts -- some species can regrow entire arms -- and fragmentation is a common method of reproduction. The fossil record of echinoderms dates back more than 500 million years.