Phylum Echinodermata

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.

Echinoderm Features:

  • Internal skeleton made of little calcium plates
  • Five-part symmetry
  • Special fluid-filled system (called a water vascular system) that operates the tube feet

Echinoderm Fact:

Sea cucumbers account for 90% of the biomass of the deep ocean floor.

Word Bank

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