The occurrence of haplosporidian parasites, Haplosporidium nelsoni and Haplosporidium sp., in oysters in Ireland

► First detection of Haplosporidium nelsoni in Irish Crassostrea gigas. ► First record of detection of Haplosporidium nelsoni plasmodia in Ostrea edulis. ► Haplosporidium sp., likely H. armoricanum, detected in Irish Ostrea edulis.