Redescription and palaeoecological significance of the bryozoan Hippoporidra patagonica (Pallaroni, 1920) in the San Julián Formation (late Oligocene) of Santa Cruz province, Argentina

Abstract

Hippoporidra is a cheilostome bryozoan that predominantly encrusts gastropod shells inhabited by hermit crabs. The genus has a Pan-Atlantic distribution and its fossil record ranges from the Eocene to Holocene. Cellepora patagonica Pallaroni is here transferred to Hippoporidra and its autozooids and avicularia are described for the first time based on scanning electron microscopy. Hippoporidra patagonica can be distinguished from the remaining species of the genus by the peculiar shape of its interzooidal avicularia and the morphology of its orifice, which is semicircular, with a straight proximal border. In addition, many specimens have adventitious avicularia located on a suboral umbo. The record of Hippoporidra patagonica (Pallaroni) in the Gran Bajo Member of the San Julián Formation (late Oligocene) in Patagonia confirms the presence of this genus at the southern tip of South America and indicates a Pan-Atlantic distribution during the Cenozoic.