Some mechanisms involved in host recognition and attachment of the glochidium larva of Anodonta cygnea (Mollusca: Bivalvia)

The ways in which the parasitic glochidium larva of Anodonta cygnea L. make initial contact with their host are investigated, and it is suggested that the thread can act as an attachment organ. Glochidia discriminate during the initial stages of attachment, and select a suitable host. Selection is achieved by the glochidia recognizing and responding to certain substances which are associated with the surface of the fish. Although these substances remain unidentified, they are almost certainly not constituents of the intact epidermal mucus. They may, however, be formed by bacterial degradation of the mucus. Prior to the formation of a cyst, a glochidium maintains its hold by grasping the host tissue between the two shell valves. The valves are held together primarily by the adductor muscle, and the hooks help to grip the host.