Despite their name starfish are not fish, but belong instead to a group of small sea creatures called echinoderms.
Sea urchins and sea cucumbers are also echinoderms.
Starfish have star-shaped bodies and are predators that prey mostly on shellfish such as scallops and oysters. A starfish uses its five strong arms to prize open its victim then inserts its stomach into the victim and sucks out its flesh.
Under the arms of a starfish are hundreds of tiny, tube-like feet. Rigger tubes inside the starfish’s Body pump water in and out of the feet, flexing the arms and driving the starfish along.
Starfish often drop some of their arms off to escape an enemy, but the arms eventually grow again.
Sea urchins are ball-shaped creatures. Their shell is covered with bristling Tines, which can be poisonous.
A sea urchin’s spines are used for protection. Urchins also have suckerlike feet for moving.
A sea urchin’s mouth is a hole with five teeth, on the underside of its body.
Sea cucumbers have no shell, but a leathery skin and a covering of talky plates called spicules.
When threatened, a sea cucumber chucks out pieces of its gut as it swims away. It grows a new one later.