Chitinozoophoran palaeoecology in the Ordovician of Öland

A special study has been made across the Arenig-Llanvirn boundary at Halludden, northern Öland, as part of an investigation of chitinozoophoran palaeoecology in the Ordovician of Öland. Chitinozoophoran ecology has been analysed with regard to 1, the general palaeogeographical conditions in the area, 2, co-occurrence with large macrobenthos and, secondarily, small macrobenthos and planktic organisms, 3, affinity to different sediments reflecting different water energy levels and to some extent depth. The chitinozoophorans were either marine benthic metazoans that attached their eggs and egg capsules to firm objects, or marine metazoans that were holoplanktic or merely planktic during the spawning season and which dispersed their eggs and egg capsules unattached in the water. The propagation bodies (so-called chitinozoans) occur commonly in shallow water limestone facies, but very high water energy seems to have been unfavourable to most of them.