There are about 7,600 living (extant) species of echinoderms and around 11,000 species that are now extinct.

The phylum Echinodermata includes starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers. They live on the ocean floor, from shallow waters near the sunlit zone near the shore to the deepest parts of the ocean in the midnight zone.

Echinoderms have some unique features:

• Spiny skin: Most echinoderms have a rough or spiny outer covering that protects them from predators.

• Radial symmetry: As adults, their bodies are usually arranged in a circle or star shape, like a starfish. However, when they are young, they have bilateral symmetry, just like humans, meaning their bodies can be divided into two mirror-image halves.

• Water vascular system: This is a special network of water-filled tubes that helps them move, breathe, and catch food.

• Tube feet: Tiny, flexible feet connected to the water system allow them to grip surfaces, move slowly, and even pry open shells of prey.

• No brain: Echinoderms don’t have a brain. Instead, a nerve ring around their central body helps coordinate movement.

• Asexual reproduction and regeneration: Many echinoderms can reproduce without mating. They can also regrow lost tissue, organs, or limbs—and in some cases, a single limb can grow into a whole new body.