Echinoderms are among the most common invertebrate animals in the marine environment in virtually any part of the world. In some places it is enough to enter a few meters from the coast, to depths of a few centimeters, to find some of the most common species of this unique group, which can inhabit the deep ocean abysses.
They are exclusively marine invertebrates, the largest edge being unrepresented in freshwater or terrestrial habitats. They always live at the bottom of the sea, at various depths ranging from the interstitial zone to the abyssal zone. They include around 7,000 living species, although it is one of the least diverse invertebrate phyla. However, this group includes well-known and symbolic animals of the marine habitat such as starfish, sea urchins, sea cucumbers, or brittle stars.
Echinoderms have great relevance both biologically and geologically. For one thing, they are among the few groups of animals that can live in the deep sea, as well as in shallow areas. They have a great capacity for the regeneration of their tissues, organs and limbs. Geologically, its characteristic internal skeleton can contribute to the generation of calcareous formations on the seabed.
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 the paranasal sinuses or lagoons.
Echinoderms also do not have developed excretory organs; on the contrary, the substances are eliminated by the vascular system of the aquifer.
Echinoderms are a group of primitive living things. Their circulatory system is open, heartless and has no organs for gas exchange or osmotic regulation, for all this they use the ambulatory system, which you can here. They have an external calcareous skeleton, except for holothurians, which have very little calcification.
Its reproduction is sexual and external. They are triblastic deuterostomes (with endo, meso and endodermis) (the mouth is formed secondarily in embryonic development). Once the egg hatches, a larva is formed, which is bilateral and free-living, undergoes several metamorphoses until the formation of the adult that is benthic. Some species of starfish can reproduce by asexual half-star division. Similarly, these species are capable of regenerating lost tentacles.
Echinoderms are hunters, they feed on gastropods that break the shell with their muscles and their beaks. Holothurians are sand filters, where they extract algae and zooplankton.
