Ultrastructural Observations on an Unidentified Cell Type Found in Epidermal Tumors of Flounders<xref ref-type="fn" rid="FN2">2</xref>

Abstract

The ultrastructure of an unknown cell type found in skin tumors of flounders is illustrated and described. The unknown cell is characterized by membrane-bound, pleomorphic, cytoplasmic granules; large mitochondria with small, round cristae; and prominent nucleoli. This cell type appears in both the stromal and epidermal portions of the tumors. Some of these unknown cells have an extracellular cell coat relatively thick, about 500 A, on cells in the stroma, but, when present on cells in the epidermis, less than one-half that thickness. In the stroma, the unknown cells frequently occur in closely connected pairs and occasionally as linked triplets or quadruplets. The unknown cell is morphologically different from any cell found in normal fish epidermis or dermis. The possibility that this cell is an altered fish cell or a unicellular parasite of unknown type is discussed.