Sea urchins - the inhabitants of the depths

On the depths of the seas with oceanic salinity abound amazing animals - sea urchins. This crawling arthropod belongs to the class of echinoderms. The hedgehog has a small body (3-30 centimeters), covered with a shell of calcareous plates, with which various needles are connected along the length. They are necessary for the animal to move. The eyes are located in the upper part of the body.

In nature there are sea urchins of the most diverse color: red, white, black, green, blue, brown, violet and gray. Some individuals change their color depending on the background of the environment. The total number of legs, equipped with suckers and located throughout the body, can be more than a thousand. They are able to stretch and contract, so that the animal can easily creep from place to place, as well as move along steep rocks. Oral opening, tightened with a delicate skin, consists of five pairs of round chewing plates, around the edges of which are external gills. Sea urchins have special organs of equilibrium - spheria. They are located near the oral opening. The sea urchin possesses special grasping organs - pedicellaria, located among the needles. They are equipped with heads with a poisonous liquid produced by special glands. The poison of the animal is very toxic. With his help, the hedgehog fights against enemies. However, this is not the only function of pedicellariae - thanks to them, the hedgehog cleanses its body of debris and various contaminants, and also captures prey and transfers it to the mouth opening.

Inhabit arthropods at depths of up to ten meters, mainly near coral reefs and coastal waters. Despite the existence of a variety of methods of protection (needles, pedicellariae, shells), animals often become prey to larger individuals, such as sea crabs, fish, mollusks, marine mammals and birds.

Reproduce the offspring of the individual begins after the third year of life. Sex cells in the arthropod are located next to the anal opening. The sea urchins may breed throughout the year. However, most often the mating season occurs during the warm season. Since these aquatic animals are dioecious, the breeding of hedgehogs occurs as follows: the female lays eggs in shallow water, after which the males fertilize it. Millions of male sex cells and testicles emitted by sea arthropods, in a few hours, turn into tiny balls covered with thin villi. Due to their oscillation, the eggs are able to turn and move in all directions. After a while, the larvae mutate: they stretch out, forming the finest limestone skeleton and four long shoots. Since this time, eggs lose their former buoyancy, and the current carries them in different directions. During the wanderings, a metamorphosis takes place. At the base of the processes and in the plethuses, a tiny sea urchin is formed and develops. At this point, the larva falls to the bottom or other surface, populating a new space. The first legs appear firmly attached to the rocks, and the animal begins to actively grow.

In coastal countries, the sea urchin is an object of fishing. In the Mediterranean states, dishes from milk and caviar of an animal are especially appreciated. However, this arthropod can be dangerous for a person. Bathe in the sea, and, accidentally stepping on the hedgehog, you can seriously damage the foot. Piercing the human skin, the needles often break, leaving the body with poisonous tips. This causes severe pain lasting several hours. Poison in some representatives of this species is very toxic.

However, the benefits of sea urchins are also indisputable. They are known as sanitarists of the sea depths, due to their ability to absorb carbon dioxide, reducing its amount in the atmosphere. The intestines of the animal are widely used in pharmaceuticals when creating medicines.