Stachelhäutern

Stachelhäutern is a German term that translates to "echinoderms" in English. This phylum of marine animals includes a diverse group of organisms characterized by radial symmetry, typically with five parts, and a unique water vascular system. Common examples of echinoderms include starfish, sea urchins, sand dollars, and sea cucumbers. They inhabit all the world's oceans, from shallow coastal waters to the deep sea.

The water vascular system is a defining feature of echinoderms. It is a network of fluid-filled canals that operate a multitude of small, retractable, tube feet. These tube feet are used for locomotion, feeding, respiration, and sensory perception. Echinoderms lack a centralized brain; instead, they possess a nerve ring and radial nerves that coordinate their movements and responses. Their skeletons are typically made of calcareous ossicles, which may be fused to form a rigid test (like in sea urchins) or be more loosely arranged (as in starfish). Reproduction in echinoderms is usually sexual, with external fertilization being common. Many species also exhibit remarkable regenerative abilities, allowing them to regrow lost body parts.