Dendritic microborings in brachiopod shells from the Silurian of the Barrandian area, Czech Republic

Four types of dendritic microborings preserved as natural casts were observed on the surfaces of brachiopod shells from the Silurian in Central Bohemia: Rhopalondendrina jakubinka isp. nov., ? Clionolithes isp., and an indeterminate dendrinid are of Llandovery (Aeronian) age, Clionolithes amoebae isp. nov. is of Ludlow (Gorstian) age. Rhopalondendrina jakubinka forms a dense plexus of thin rhizoidal tunnels extending from a broad and curved entrance tunnel. ? Clionolithes isp. forms characteristically rarely branching thin meandering tunnels with a globular central node, while C. amoebae forms rosette-like microborings with sinuously curved primary branches and scarce lateral branches of smaller size. Microborings are present both on outer and inner surfaces of shells; their location and number confirm massive infestation of dead shells which were exposed on the sea floor for long time intervals and which were not affected by mechanical abrasion of the shells. This indicates narrow ecological limits for these endobionts, most likely within the deeper euphotic zone.