These globular marine invertebrates move very slowly along the seabed. There are about 700 different species of sea urchins worldwide. Many sea urchins have venomous spines. Adult sea urchins have five-sided radial symmetry. Their skin has hard, chalky plates, and is called the test.
Sea urchins have a globular body and long spines that radiate from the body.
The spines are used for protection, for moving,and for trapping drifting algae to eat. Among the spines are five paired rows of tiny tube feet with suckers that help with locomotion, capturing food, and holding onto the seafloor. Tiny pedicellarines are small stinging structures that are used for defense and for obtaining food. Like all echinoderms , sea urchins do not have a brain. The anus and the genital pores are on the top of the sea urchin.