Ordovician to Holocene | image = Haeckel Ophiodea.jpg | image_caption = "Ophiodea" from Ernst Haeckel's Kunstformen der Natur, 1904 | domain = Eukarya | regnum = Animalia | phylum = Echinodermata | subphylum = Asterozoa | classis = Ophiuroidea | classis_authority = Gray, 1840 | subdivision_ranks = Orders | subdivision = ME Oegophiurida Ophiurida Phrynophiurida }} Brittle stars, or ophiuroids, are echinoderms, closely related to sea stars. They crawl across the seafloor using their flexible arms… (More on Ophiuroidea)