Survival of heterotopic headfoot transplants in Biomphalaria glabrata (Mollusca : Pulmonata)

The entire headfoot (HF) of small snails, Biomphalaria glabrara, was implan ted into the hemocoel of allogeneic adults and examined histologically at 3 0 and 60 days postimplantation (DPI). Although displaying varying degrees o f abnormal morphology, the HF allografts continued feeding motions with the buccal mass and showed muscular contractions of the foot muscle. The trans ected esophagus fused shut and became distended with amorphous material, po ssibly ingested and/or secreted substances. The buccal mass grew, and piece s of the exfoliated radular ribbon were found in the esophageal sac. Althou gh most major structures of the HF appeared quite normal at the cell and ti ssue level, the tentacles and epithelium covering the dorsal and lateral su rfaces of the HF apparently were lost when in direct contact with the recip ient's hemolymph, but persisted if folded or invaginated below the implant surface. No host hemocytic response was observed at either 30 or 60 DPI. Th ese results demonstrate not only considerable physiological plasticity by t he implant but also immunological tolerance to histologically complex allog rafts by the recipient, and support the hypothesis that allorecognition is poorly developed in molluscs.