Anatomy: The body of the sea cucumber is elongated, leathery and muscular; spines are contained with the skin. These echinoderms have no arms, but do have five-part symmetry. Surrounding the mouth are 8 to 30 tentacles (modified tube feet). Five double rows of tube feet (with tiny suction cups) run along the body; they are used for crawling along the sea bed or anchoring to a rock. A sea cucumber breathes by pumping sea water in and out of an internal organ called a respiratory tree. Some sea cucumbers burrow into the sea floor. Sea cucumbers have no brain. The biggest sea cucumber, the tiger's tail sea cucumber (Holothuria thomasi), is about 2 m long - most sea cucumbers are much smaller than this.

Diet: Sea cucumbers eat decaying matter that floats in the water or is in the sand.

Enemies: Sea turtles, crustaceans, many fish, and people eat sea cucumbers. Sea cucumbers can expel most of their internal organs to confuse predators - they later regrows the organs. Some sea cucumbers' bodies contain toxins that can deter attackers.

Reproduction: Eggs and sperm are broadcast (released) into the water (the sexes are separate). When an egg is fertilized and hatches, the tiny planktonic larva drifts with the ocean currents. It will eventually settle onto the sea floor and develop into an adult.

Classification: Kingdom Animalia (animals), Phylum Echinodermata (echinoderms), Subphylum Asterozoa (=Eleutherozoa - sea cucumbers, sea urchins, sand dollars, sea stars, brittle stars, and basket stars). Class Holothuroidea (sea cucumbers), about 900 species.