Echinodermien

Echinodermien, or echinoderms in English, are a phylum of marine animals characterized by a calcareous endoskeleton, a water vascular system, and pentaradial symmetry as adults. They are deuterostomes, closely related to chordates, and live primarily in marine environments from shallow coastal waters to deep seas.

Five extant classes make up the living echinoderms: Asteroidea (starfish), Echinoidea (sea urchins and sand dollars), Holothuroidea (sea cucumbers), Crinoidea (sea lilies and feather stars), and Ophiuroidea (brittle stars). Most species inhabit the oceans worldwide, with a broad range of habitats including rocky shores, coral reefs, seagrass beds, and soft sediments.

Anatomy and physiology: Echinoderms possess an internal skeleton made of calcareous plates. A distinctive feature is the water vascular system, which powers tube feet used for locomotion, feeding, and respiration. Adult echinoderms typically exhibit fivefold radial symmetry, though their larvae are bilaterally symmetric. They lack a centralized brain, instead having a nerve ring around the mouth and radial nerves in the limbs. Mutable connective tissue allows echinoderms to change tissue stiffness rapidly.

Ecology and biology: They occupy diverse ecological roles as grazers, detritivores, filter feeders, and predators, contributing to nutrient cycling and habitat structure. Reproduction is usually sexual, with separate sexes and external fertilization; many species have free-swimming larval stages before reaching their adult form.

Evolution and conservation: Echinoderms have a rich fossil record dating back to the Early Cambrian. They are sensitive to ocean acidification and habitat disturbance, making them indicators of marine ecosystem health and subjects of conservation concern.