DK Nature: Echinoderms
Starfish, brittle stars, sea urchins, and sea cucumbers all belong to the family of echinoderms. These slow-moving, headless invertebrates are the only animals with bodies based on a five-pointed structure. All echinoderms live in salt water.
Sea urchins live on the seabed or buried in sand. Like starfish, they have many tiny tube feet, which they use for crawling and feeding. Sea urchins are well protected by their sharp spines.
Starfish feed by turning their stomachs inside out over their victims. They then ooze digestive juices, which dissolve their prey. Most starfish eat shellfish such as mussels. They move in search of food using the tiny, flexible tube feet that protrude from their underside.
Starfish that lose limbs can grow new ones in their place. If a severed limb contains certain cells, it too can survive and will eventually grow into a whole new starfish. Losing a limb may help a starfish escape from a predator’s clutches. Brittle stars are so called because their limbs break off easily.
The phylum of Echinodermata includes about 6,000 species, divided into six classes:
| Sea lilies and feather stars |
| Starfish |
| Brittle stars and basket stars |
| Sea cucumbers |
| Sea urchins |
| Sea daisies |
