A new ophiuroid (Geocoma schoentalensis sp. nov.) from the Middle Jurassic of northwestern Switzerland and remarks on the family Aplocomidae Hess 1965

A new ophiuroid species from the Hauptrogenstein Formation (Middle Jurassic, Bajocian) of the Rehhag ridge near Schöntal, northwestern Switzerland, is described based on 34 specimens. The impression of an indeterminate astropectinid sea star has also been found. The fully articulated specimens have been smothered by mobile oolitic dunes or sandwaves. The site can be genetically classified as an obrution deposit and belongs to the widely recognized “Hauptrogenstein type”. The remains are assigned to the genus Geocoma d’Orbigny 1850, best known from the type species, G. carinata (Münster), from the Tithonian Plattenkalk of Zandt. As suggested by Kutscher (1997) this species also includes Ophiocten kelheimense Boehm 1889, now documented by numerous well-preserved specimens from the Plattenkalk of Hienheim. Kutscher assigned the Hienheim specimens to the genus Sinosura Hess 1964 and used both names though G. carinata has priority. Despite rather small differences Sinosura is retained as a valid genus besides Geocoma, and both are placed in the family Aplocomidae Hess 1965. Geocoma and Sinosura share small adpressed arm spines with Aplocoma d’Orbigny 1852. Aplocoma is represented by a number of Triassic and Jurassic species, and the subfamily Aplocominae is proposed herein for the three genera. A second subfamily, Ophiopetrinae, is proposed for the genera Ophiopetra Enay &; Hess 1962 and Ophiohybris Hess 1964, and is characterized by larger, erect arm spines.