échinodermes

Échinodermes is a phylum of marine invertebrates that encompasses a diverse group of animals known for their radial symmetry, typically pentaradial (five-part) as adults. This phylum includes well-known creatures such as starfish, sea urchins, sand dollars, sea cucumbers, and brittle stars. Their bodies are characterized by a unique water vascular system, a network of fluid-filled canals and tube feet that is used for locomotion, feeding, respiration, and sensory perception. Unlike most other animals, echinoderms lack a distinct head and possess an endoskeleton made of calcareous ossicles, which can be fused into a rigid test or remain more loosely arranged. Reproduction in echinoderms is primarily sexual, with external fertilization being common, and they exhibit remarkable regenerative abilities, with some species capable of regrowing lost limbs or even entire bodies from fragments. Their ecological roles are varied, with many serving as important predators or grazers, influencing the structure and dynamics of marine ecosystems. The fossil record of echinoderms dates back to the Cambrian period, indicating their long evolutionary history.