There are basically three ways for starfish to feed:

1. Most starfish have long and flexible wrists, and there are suckers on the tube feet. Most of them feed on bivalves. When they feed, their bodies are on the shells, and their wrists are sucked on both sides of the shells. Due to the vacuum effect of the suckers at the end of the tube feet, the pulling force is enough to open the shell mouth of bivalves, and the starfish immediately turns out of the spouted stomach and inserts it into the shell mouth, and secretes digestion.

2. Some species with short wrists and no sucker on the tube feet feed on smaller animals, such as small crustaceans. When feeding, the whole food is swallowed and digested in the stomach instead of in vitro.

3. The species living in the deep sea feed by cilia filtration, and the sediment and organic matter falling on the body surface are swept into the step ditch by cilia action to form food rope, and then sent into the mouth, such as Acer starfish. Another example is Henricia, which has cilia in the gastric caecum, and relies on the movement of cilia to help suck food into the stomach.

Extended information:

Starfish's mouth is under its body. Its digestive system includes two stomachs, one of which can be ejected from the body, enveloping and digesting food outside the body. This external digestive function of starfish enables it to eat animals much larger than its mouth, including all kinds of shellfish and sea cucumbers, arthropods and small fish. Semi-digested food is sent to the other stomach in the body to continue digestion and absorption. Because starfish need a lot of digestive ability, they also have many digestive tubes in their arms.

Starfish is one of the animals that can regenerate rapidly. If one of the tentacles of a starfish is cut off, it will grow back in a short period of time, and the tentacles cut by a few starfish will grow into a starfish, which has the characteristics of earthworms, lizards, lobsters, polyps, snails and the most regenerative worms. Sometimes starfish will deliberately throw off their tentacles for defense.

Environmental value of starfish:

The Leibniz Institute of Oceanography in Germany once published a communique, saying that the latest research found that echinoderms such as starfish play an important role in the marine carbon cycle, and they can directly absorb carbon from seawater in the process of forming exoskeletons.

Echinoderm is an invertebrate living on the seabed, which can be divided into five categories: starfish, sea urchin, ophiopoda, sea cucumber and sea lily, and its figure covers all oceans. Studies have found that echinoderms absorb carbon from seawater and form exoskeletons in the form of inorganic salts (such as calcium carbonate). After their death, most of the carbon-containing substances in their bodies will remain on the seabed, thus reducing the carbon entering the atmosphere from the ocean. In this way, echinoderms absorb about 1 million tons of carbon every year.

It has been known before that the acidity of seawater will rise after the greenhouse gases produced by burning fossil fuels enter the ocean, which will harm coral reefs and shellfish. This time, the researchers found that acidic seawater is also very harmful to echinoderms, making it impossible for such creatures to form a solid calcium-containing exoskeleton.

Baidu encyclopedia-starfish (echinodermata starfish)