probably by shortening (with conformation to -oid entry 1) of New Latin Ophiuroidea, class name, from Ophiura, a brittle star genus (from Greek óphis "snake" + -oura, feminine of -uros "having a tail [of the kind specified]," adjective derivative of ourá "tail") + -oidea, suffix of higher taxa (from -oides -oid entry 2 + -ea, neuter plural of -eus -eous) — more at ophidian, ass entry 2
Note: The genus name Ophiura was introduced by Jean-Baptiste lamarck in Système des animaux sans vertèbres (Paris, 1801), p. 350, as a renaming (Ophiura lacertosa) of Linnaeus's Asterias ophiura (Systema naturae, 10th edition, 1758, p. 662). Linnaeus, in turn, based the epithet on a description of a brittle star in the posthumously published Plantae per Galliam, Hispaniam et Italiam observatae (Paris, 1714) by the Dominican friar and naturalist Jacques Barrelier (1606-73), with the heading "Stella marina, οφιόκνημος seu οφιούρος" ("sea star, ophióknēmos [snake-legged] or ophioúros [snake-tailed]").