Poster

Previous studies of the genus Zalophotrema have been confined to its taxonomy and definitive host types. I have described the ultrastructure of the sensory receptors of the miracidia of Zalophotrema hepaticum.

Living adult Z. hepaticum were removed from the bile ducts of adult California sea lions, Zalophus californianus. Eggs were transferred from the adult flukes to sea water and maintained in an incubator until they hatched. The miracidia were prepared for transmission electron microscopy.

The apical papilla contains several uniciliated endings. Six anterior papillae are located at the base of the apical papilla. One pair of lateral papillae and 4 sheathed uniciliated nerve endings are located between the first and second tiers of epithelial cells. Two of the uniciliated endings are associated with the lateral papillae. One of these endings is dorsal to one papilla, and the other is ventral to the remaining papilla. Both of the uniciliated endings possess a cytoplasmic knob on the papillar side of the sheath. It is suggested that these 2 structures associate to perform a georeceptive role.

Sensory receptors are used by miracidia to find a suitable host. The results suggest that Z. hepaticum miracidia use chemo-, tango-, and georeception to locate their first intermediate host.

Acknowledgements

This study was sponsored by the Science and Engineering Research Council of the UK (Overseas Award Ref. 9060024X). I wish to thank the staff and volunteers of The Marine Mammal Center, Sausalito, CA and Dr. M. Dailey, Dr. T. Douglass, Dr. I. Jones, and Dr. E. Platzer for their assistance with this work.