A New Type of Early Cysticercoid Stage in a Cyclophyllidean Cestode

Abstract

CYSTICERCOIDS of various cyclophyllidean families are known to occur in small invertebrate hosts, commonly in arthropods and very occasionally in molluscs and annelids. During the course of some work on the pulmonate snail, Oxychilus cellarius (Müll) one of us noted a 3 per cent infection of the peritoneum around the digestive gland and gut with cysticercoids of what we believe to be a member of the Dilepididae, the first such record from a mollusc. The cysts numbered from one to about fifty in a single specimen and were seen in various stages of development, ranging from what we consider to be the pre-cystic stage to the fully formed, infective cysticercoid. The older cysticercoids with completely formed scolex and bladder resemble very closely the corresponding stage of another cysticercoid of the Dilepididae—that of Choanotaenia infundibulum (Bloch) described by Reid and Ackert¹. A full account of these stages will be published later, but meanwhile we wish to direct attention to the earliest stage of this cysticercoid—a form which we regard as being pre-cystic and which, so far as we are aware, is unlike anything previously described.