Bimineralic (calcareous and phosphatic) skeleton in Late Ordovician Bryozoa from Sardinia: Geological implications.

The study of Palaeozoic Bryozoa from the Upper Ordovician of Sardinia was carried out by integrating the traditional thin section description with the SEM observation of single zooecia or zoarial remnants, isolated by acid acetic technique. This technique was made possible by the presence of a bimineralic (calcareous and phosphatic) skeleton,which is interpreted as the result of the mineralization of the membranous part of the cryptocyst originally very rich in phosphorus. The frequent records of phosphatic bodies in Bryozoa lead us to hypothesize the possibility that some Bryozoa secrete,at least in the Palaeozoic, a phosphatic skeleton in response to particular environmental conditions. The deposition of calcium phosphate occurred in the zooecial cavity owing to the change in chemical conditions between the regeneration and degeneration phases.