The echinoderms (Echinodermata) are marine metazoan animals having an exoskeleton with granules scattered calcareous or calcareous plates juxtaposed. Sometimes these plates have spines. On the other hand, echinoderms are characterized by their pentagonal radiated symmetry (a body with five regions around a central disk).
The dermoskeleton has small holes from which appendages emerge that can end in a suction cup. Said appendices are organized in radial series. Echinoids and asteroids also have pedicellars, which are pincer-shaped structures to eliminate larvae that try to adhere to the body, attack prey or defend themselves from predators.
Specialists affirm that there are about 7,000 species of echinoderms at present, which are added to another 13,000 already extinct. All live in the marine environment and are unable to subsist in fresh water or on land.
Among the peculiarities of echinoderms, it should be noted that they lack a heart, since the circulatory system is open and the blood vessels are in connection with sinuses or lagoons.
Echinoderms also do not have developed excretory organs; on the contrary, the substances are eliminated through the aquifer vascular system.
In terms of their mobility, most echinoderms can crawl and swim thanks to the movement of their arms. Generally, mobility is slow and smooth.
Finally, it can be mentioned that its reproduction is sexual. However, some species can reproduce asexually through one of their arms. This is possible only when the arm contains a part of the central disc.
Some species of the group
Among the numerous species that exist within this group, the following are some of the best known and studied.
* The sea urchin is one of the species cataloged within the Echinodermata phylum, in which those animals with spiny skin are located. It has a round body that is stuffed with thorns (like the terrestrial hedgehog); they can measure up to 20 cm depending on the species and can be extremely harmful against its aggressors. On the lower surface, the hedgehog has a mouth and on the upper surface the anus. It feeds on algae, which it extracts from rocks using its jaw system.
* The starch is one of the most particular echinoderms, since it feeds on other animals. It has five long, extremely thin arms with thorns that serve to capture its victims. Its main source of food are certain mollusks, small crustaceans and other small animals. They also have the ability to regenerate those parts of the body that they may lose.
* The language of flamenco, scientifically called holothuria, and belongs to those thousands of marine animals that live thanks to the microhabitat created around coral reefs.
* The crown-of-thorns star represents a danger to marine reefs as it feeds on coral and an overpopulation of this species endangers the survival of the microhabitat. They have a mouth covered with radial arms, where each one has a row of ambiulacral feet that allow them to move from one place to another with ease.
* The brown sea cucumber is evolutionarily related to the starfish, the sea urchin and the sea lilies. The diet of these animals is based on planktonic organisms and to catch them they use their tentacles that are surrounded by mucus for this purpose.