Unbranched Holdfasts of Stemmed Echinoderms from the Ordovician of the Leningrad Region

Based on examination of the collection of stemmed echinoderm holdfasts from the Ordovician of the Leningrad Region (Russia), all holdfasts are divided in two large groups: “unbranched” and “branched”. In total, 11 morphotypes of unbranched holdfasts are identified and described in detail.