Streptoiocrinus gen. nov. (Disparida, Crinoidea) from the Lower and Middle Ordovician of the Leningrad Region, and Fluctuating Asymmetry of Radial Symmetry

A crown of Streptoiocrinus gen. nov., with its articulated stem, the columnals of which have long been known in the Billingen and Volkhov regional stages (Floian and Dapingian stages) of the Leningrad Region and Estonia are described. A detailed study of the crown and stem morphology showed that the new genus belongs to the disparid crinoid superfamily Ioсrinacea. This genus is the first mass crinoid invader into the Ordovician Baltic paleobasin. The fluctuating asymmetry in the manifestation of the pentaradial symmetry of the stem columnals is described.