Observations on the ultrastructure of large cells associated with putative neoplastic disorders of mussels,Mytilus edulis,from Yaquina Bay,Oregon

Large cells, generally thought to be associated with neoplastic disorders in bivalve mollusks, were studied with the electron microscope. The atypical cells had an average diameter of 15 μm and a nuclear to cytoplasmic ratio of about 1–1.5. Nuclei were extensively pleomorphic and bizarre shapes were common. Nucleoli were prominent and often multiple. In the cytoplasm of the large cells, there was a wide range of variability in anomalous organelles. Two cell types were originally thought to exist; however, it is now thought that the two cell types represent the two extreme morphological expressions of a single cell line. Their varying appearance is correlated with the density of ribosomes and abundance of cellular organelles. The large Mytilus edulis cells possess many ultrastructural properties that are characteristic of certain malignant vertebrate cells. However, alternative explanations for their structure and function are also possible.