What are echinoderms?
Q: What are echinoderms?
A: Echinoderms are a successful phylum of marine animals that includes sea stars, brittle stars, sea urchins, sea cucumbers and their relatives.
Q: What features do echinoderms have?
A: Echinoderms have a skeleton of plates formed from calcite (a mineral made of calcium carbonate), five-rayed (pentameral) symmetry, a water-vascular system (an internal system of tubes and bladders filled with water), tube feet (extensions of the water-vascular system used for walking, respiration and feeding) and stenohaline characteristics which prevent them from handling big changes in salinity.
Q: Where do echinoderms live?
A: Echinoderms are entirely marine and live in all parts of the ocean, mostly on the sea floor. Some filter feed while others (starfish) are important predators of molluscs and other shell-fish. They can be found near the shore or on reefs.
Q: How long has this phylum been around?
A: This phylum appeared in the early Cambrian period and contains about 7,000 living species as well as 13,000 extinct species.
Q: Are there any subgroups within this phylum?
A: Yes - some authorities refer to four or five main groups as subphyla while others call them classes.
Q: Is this group exclusively marine?
A: Yes - no animals in this group live on land or in fresh or brackish water; they are entirely marine creatures.
