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

The entire headfoot (HF) of small snails, Biomphalaria glabrara, was implanted into the hemocoel of allogeneic adults and examined histologically at 30 and 60 days postimplantation (DPI). Although displaying varying degrees of abnormal morphology, the HF allografts continued feeding motions with the buccal mass and showed muscular contractions of the foot muscle. The transected esophagus fused shut and became distended with amorphous material, possibly ingested and/or secreted substances. The buccal mass grew, and pieces of the exfoliated radular ribbon were found in the esophageal sac. Although most major structures of the HF appeared quite normal at the cell and tissue level, the tentacles and epithelium covering the dorsal and lateral surfaces of the HF apparently were lost when in direct contact with the recipient's hemolymph, but persisted if folded or invaginated below the implant surface. No host hemocytic response was observed at either 30 or 60 DPI. These results demonstrate not only considerable physiological plasticity by the implant but also immunological tolerance to histologically complex allografts by the recipient, and support the hypothesis that allorecognition is poorly developed in molluscs.