Abstract. Preserved valves of fossil glochidia have been recovered from Holocene lake marls at Quidenham Mere, UK. Detailed morphological comparisons with glochidia removed from live adult unionids have enabled confident identification of the fossil glochidia as those of Anodonta anatina. Fossil glochidia are potentially powerful tools in the interpretation of palaeoenvironments. Different species of freshwater mussels are known to release glochidia at different times of the year and, therefore, the occurrence of fossil glochidia can provide information on the season during which sediments accumulated. Furthermore, glochidia can provide information on the presence of certain fish species and on water depth.