Sea stars are marine creatures, many people think they are not like animals, but in fact they are marine animals, and they are also carnivores. Its "five-pointed star" shape is the most obvious feature that people remember it.
A starfish is an echinoderms. It belongs to this big family along with sea cucumbers and sea urchins. Sea stars always look soft, but they actually have a hard covering on the upper half of their skin, which is made of calcium carbonate plates with tiny spines on the surface. This is their unique protective armor, which protects them from predators.
The starfish we see are all lying quietly on the bottom of the sea, and they have no feet. But if you turn it over, you will find that it has a lot of small tube feet on its body, and there is a suction cup at the front end of these tube feet. If the starfish wants to walk forward, it will perform a suction and release action through the suction cups on the tube feet, so that it can move forward. But the speed is very slow, basically only a few centimeters per minute. As such, it feels like it's always standing still.
The starfish has no independent circulatory system, and its body cavity is mainly composed of seawater, so it has no blood. Seawater is pumped into the animal's hydrovascular system through the sieve plate, and starfish can only survive in seawater due to the isotonicity of coelom fluid and seawater.
Many people just look at the appearance of a starfish and think it has no eyes. But in fact, most of the vital organs of the starfish are actually in its five horns, including the eyes. But its eyes are different from the concept of eyes that we ordinary people understand. Its eyes are at the ends of the five corners and have a simple structure. Eyes don't help starfish see objects completely, they can only distinguish between light and dark.
Although starfish are ordinary, they are carnivores. The speed of starfish is generally relatively slow, so they can eat fewer types of animals, because they can't prey as quickly as other fish. Generally speaking, the objects they prey are some slow-moving animals, such as shellfish, crabs, and sea urchins.
In addition, starfish have significant environmental value. The Leibniz Institute of Oceanography in Germany has published a bulletin saying that the latest research has found that echinoderms such as starfish play an important role in the ocean carbon cycle, and they can directly absorb carbon from seawater in the process of forming exoskeletons. Also, when they die, most of the carbon-containing material in their bodies remains on the seafloor, reducing the amount of carbon that enters the atmosphere from the ocean. Through this pathway, echinoderms absorb approximately 100 million tons of carbon per year.