Echinoderms - Sea Urchins

The Echinoderms include the Echinoids (Sea Urchins), Holothuroids (Sea Cucumber), Asteroids (Starfish ), Crinoids (Sea Lilies), as well as the extinct Blastoids, Cycstoids, and Carpoids.

Echinoids (Sea Urchins)
The Echinoids possess a rigid, globular skeleton made up of columns of thin, calcite plates (ambulacrals and interambulacrals). The plates known as ambulacrals have small pores for tube feet. All plates have swollen tubercles for the ball-and-socket articulation of spines, which are used for defence and some-times for walking. Regular Echinoids, which forage on the sea bed show radial symmetry; irregular Echinoids, which usually burrow in soft sea beds, show bilateral symmetry.