Les ophiures (Ophiuroidea) sont des échinodermes voisins des astéries (ou étoiles de mer). Ils se nourrissent principalement de jeunes mollusques et d'annélides. Leurs cinq bras sont fins, le disque central est bien individualisé et ils ne possèdent pas d'anus (rejet par la bouche).
Echinoderms (Phylum Echinodermata from Greek, ἐχῖνος, echinos – "hedgehog" und δέρμα, derma – "skin") are a phylum of marine animals. The adults are recognizable by their (usually five-point) radial symmetry, and include such well-known animals as starfish, sea urchins, sand dollars, and sea cucumbers. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes (a superphylum), after the chordates (which include the vertebrates, such as birds, fish, mammals, and reptiles). Echinoderms are also the largest phylum that has no freshwater or terrestrial (land-based) representatives.
Aside from the hard-to-classify Arkarua (a Precambrian animal with Echinoderm-like pentamerous radial symmetry), the first definitive members of the phylum appeared near the start of the Cambrian period. The word "echinoderm" is made up from Greek ἐχινόδερμα (echinóderma), "spiny skin", cf. ἐχῖνος (echínos), "hedgehog; sea-urchin" and δέρμα (dérma), "skin", echinodérmata being the Greek plural form.