Ophiuroidea note details
A.M. Clark (1967) proposed to the ICZN to suppress the older name O. pentaphylla in favour of the more widely applied name fragils. That proposal seems never to have been decided and technically, O. pentaphylla has priority. Since O. fragilis has been in prevailing usage for about a century, changing that would cause instability. However, the article on prevailing usage does not apply because the name pentaphylla has been used after 1899.
Clark, A.M. 1967. Proposals for stabilization of the names of some common European Ophiuroidea Z.N.(S.) 1772. Bulletin Zoological Nomenclature, 24(1), 41-49. available online at http://www.biodiversitylibrary.org/page/12223192#page/59/mode/1up