Well-preserved and diverse radiolarian assemblages were recovered from a continuous 95 m-thick Lower Jurassic succession of grey siliceous limestone and marl on Mount Rettenstein (Northern Calcareous Alps, Austria). A total of seven radiolarian samples across the Late Sinemurian-Early Pliensbachian boundary were studied - five samples were assigned to the Upper Sinemurian and two samples to the Lower Pliensbachian. In total, 188 radiolarian species have been identified. In this article, we present 90 species and 33 genera belonging to the order Nassellaria. One genus and five species are described as new: Katroma hasta Cifer nov. sp., Tipiforma missoniae Cifer nov. gen. nov. sp., Trexus rotundus Cifer nov. sp., Wrangellium mediterraneum Cifer nov. sp., and Zhamoidellum spinosum Cifer nov. sp. In the Sinemurian, the most abundant nassellarian genera are Droltus, Parahsuum and Saitoum . The Pliensbachian yields an entirely different nassellarian assemblage dominated by the genera Zhamoidellum and Lantus . Compiled stratigraphic and geographic ranges as well as a synonymy, descriptions and remarks are provided.
