Starfish, like sea cucumbers and sea urchins, are echinoderms. They usually have five arms, but there are also four or six, mostly star-shaped. The entire body is composed of many calcium bone plates and connective tissue. There are protruding spines, tumors or warts and other appendages on the surface, some with as many as 50 wrists.

The starfish is a greedy carnivore. Its tentacles are its sharp teeth for feeding. When it is alive, its mouth faces downwards and its anti-mouth faces upwards. There is a walking groove on the ventral side of the wrist, and a tube protrudes from the groove. They use their tube feet to capture prey and allow themselves to cling to rocks.

Starfish like to eat molluscs, but due to their slow movement, their main prey are some slower-moving marine animals, such as shellfish, sea urchins, crabs and sea anemones. Different types of starfish There will be some differences in what you eat.

When starfish hunt, once they find prey, they often adopt a slow and roundabout strategy. After approaching, they will put their tentacles on the prey to prevent the prey from escaping. They can also use their tentacles to open the shell and stretch out the bottom of the shell. The stomach digests prey.

When most starfish actually eat, they actually turn their stomachs out, or spit out the stomach pouch from their mouths, and then use digestive enzymes to dissolve the prey outside their bodies and be absorbed by them.

For starfish living in the deep sea, they use cilia to filter food. The action of cilia sweeps the sediment and organic matter that has fallen into the body surface into the step groove, forming a food cord, and then sends it into the mouth.

For some species of starfish with short arms and no suckers on the tube feet, they feed on smaller animals, such as small crustaceans. When feeding, they swallow the food whole and digest it in the Intragastric rather than externally.