Epizootic Neoplasms in the Clam Macoma balthica (L.) From Chesapeake Bay

Summary

Histologic examination of a wild population of Macoma balthica in Chesapeake Bay revealed the presence of a highly invasive neoplasm. The lesion was characterized cytologically by a high degree of anaplasia. Local lesions originated in gill epithelia and spread across basement membranes to produce a diffuse systemic disease and discrete localized neoplasms in other organs. The disorder was most prevalent during the winter months and not found during the summer. Clams from affected populations closely observed had high mortality rates. This disorder may have been the first highly invasive spontaneous neoplasm of probable epithelial origin described from the class Pelecypoda. Study of this epizootic provided valuable insights into the seasonality, progressive development, and lethality of the disease.