Includes: Sea Stars, Sea Lilies, Sea Urchins, Sea Cucumbers, and Brittle Stars
The majority of animal body plans are bilateral with both sides of their bodies the same. And they have a distinct head and tail. Echinoderms do not follow this pattern. Many begin life as a bilateral larva. But later, they change completely and become circular with five-part symmetry.
The bodies of echinoderms are made of tiny, hard calcium-based plates. The plates are often spiny and always covered by a thin skin. Because the echinoderm skeleton is on the inside, it is called an endoskeleton. Echinoderms seem little more than a skeleton of tiny plates and water.
Echinoderms don’t use large muscles working on body parts like many other animals. Instead, they move, feed and breathe with a unique water-vascular system. The system ends in hundreds of water-filled tube feet. This doesn’t produce high-speed movement. Most move so slowly that, by our standards, they appear to be nearly stationary. Echinoderms are, however, prominent members of the marine environment. They are exclusively marine animals.
- Internal skeleton made of little calcium plates
- Five-part symmetry
- Special fluid-filled system (called a water vascular system) that operates the tube feet
Sea cucumbers account for 90% of the biomass of the deep ocean floor.
Bilateral: the right and left sides are the same
Larva: the active, immature form of an animal
Five-Part Symmetry: arrangement of five similar parts on around a central point
Water-vascular: this fluid-filled system provides the water pressure that operates the animal’s tube feet