Exceptionally well‐preserved brittle stars from the Pliensbachian (Early Jurassic) of the French Ardennes

Abstract

Abstract: Two new genera and species of ophiuroid, Inexpectacantha acrobatica new gen. et sp. and Eirenura papillata new gen et sp., are described on the basis of 39 articulated specimens and several hundreds of arm fragments and isolated skeletal parts. The material was extracted from a lumachellic bed in a late early Pliensbachian succession of argillites at Sedan, French Ardennes. The material is unusually well preserved with even finest structures of the skeleton discernible. Despite the exceptionally detailed morphological data extractable from the material, the higher taxonomic classification in the system of recent ophiuroids could only be tentatively attained. Inexpectacantha acrobatica seems best placed within the Ophioplinthacinae inside the Ophiacanthidae whereas Eirenura papillata shares greatest similarities with the Ophioleucinae. The occurrence of articulated specimens of different sizes, with some of the most delicate skeletal structures left intact, together with completely disarticulated skeletons of the same species suggests that the ophiuroids were preserved as autochthonous faunule among an in situ population of Modiolus sp. during a period of more favourable bottom water conditions in an otherwise largely hostile near‐shore soft‐bottom environment. Based on its small size, the highly flexible arms and the presence of well‐developed hooks on distal arm segments, an epizoic way of life is inferred for I. acrobatica while E. papillata, with its rigid arm structure and the conspicuously large tentacle pores, is interpreted as mostly deposit‐feeding bottom surface dweller.