Ordovician and Silurian holothurians (Echinodermata)

A synopsis of Ordovician and Silurian helothurians is given and the arguments for the limited knowledge of this echinoderm class are discussed in detail. New findings of holothurian sclerites and pieces of the calcareous ring from Ordovician glacial erratic boulders (geschiebe) and the Silurian of Gotland are presented and figured. The oldest known holothurian sclerites come from Llanvirnian strata, and the oldest pieces of the calcareous ring are of Ludlovian age (Gotland, Sweden).