The mucron of the gregarine Digyalum oweni (Protozoa: Apicomplexa), parasitic in Littorina species (Mollusca: Gastropoda)

The aseptate gregarine Digyalum oweni is parasitic in the gut of some species of Littorina, marine gastropod molluscs. The mucron, its anterior attachment organelle, comprises a ring of lobes and a ring of granular material embedded in the apex of the host intestinal cell. Some tissue damage is caused to the host cell but this is confined to the apical tip and otherwise the parasite does not appear to harm the snail. In addition to securing the parasite to its host, the mucron may have a role as a microtubule organizing centre and in nutrition.