The trace fossil Arachnostega in the Ordovician of Estonia (Baltica)

In the Ordovician of Baltica, burrows assigned to the ichnogenus Arachnostega Bertling, 1992 occur in steinkerns of bivalves, cephalopods, gastropods and hyolithids. Arachnostega abundance decreased significantly during the Ordovician in Baltica. It was most abundant in the Darriwilian (17% of gastropod steinkerns), slightly less abundant in the Sandbian (11% of gastropod steinkerns) and least abundant in the Katian (3% of gastropod steinkerns). This change in Arachnostega abundance correlates well with the regional climatic change (from temperate to tropics) during this interval, along with resulting changes in sedimentary environment, geochemistry and biota. Arachnostega was substrate selective and preferred bivalves over gastropods. Arachnostega occurs only in the Middle and Upper Ordovician of Estonia and is absent in the Lower Ordovician.