protopterygian,a.Ichth.|ˌprəʊtəʊptəˈrɪdʒɪən| [f.Gr. πρωτο- proto- + πτερύγιον fin + -an.] Introduced by Ryder to designate the first-fin stage when the embryonic fin rays first appear. 1884Rep.U.S.Comm. Fish. (1886) 987 The protopterygian stage of development of the permanent fin-rays.