Sea urchins are echinoderms. Echinoderms mainly refer to those with radiation symmetry outside the body and water pipe system inside the body. These two sea urchins are available, so they belong to echinoderms. Sea urchins live in a wide range, some of which are distributed in shallow sea areas, and some of which live under several kilometers of sea areas, but most of them are distributed in shallow sea areas.

Most people think of sea urchins as plants, but they are not. Sea urchins are invertebrates. They can move in the sea, but they don't move fast. Moreover, sea urchins like to eat some aquatic animals, such as hydra and worms in the sea. Of course, if there is not enough food, they will also eat some algae, moss and so on.

There are many varieties of sea urchins, most of which are poisonous. However, different sea urchins have different locations of toxins. Some sea urchin toxins are on the reproductive organs, and some sea urchin toxins are on the thorns. The toxins of sea urchins are still quite harmful to human beings. If they are accidentally pricked by the thorns of sea urchins, they may have difficulty breathing or even respiratory failure. Sea urchins, for example, have barbs on their spines. If these barbs penetrate the skin, they may cause redness and swelling. If it is serious, it will also affect the heartbeat and may even lead to spasms.