Composition and ultrastructure of elasmobranch granulocytes. II. Rays (Rajiformes)

Abstract

The blood granulocyte composition of seven species of ray is given together with ultrastructural observations made on the epigonal organ and blood of Pavoraja spinifera and the spleen of a deepwater rajid skate. Under the light microscope three granulocyte types, eosinophils, eosinophilic granulocytes and neutrophilic granulocytes could be distinguished. At the EM level two granulocyte types were apparent, one with elongated granules containing longitudinal fibrils that consolidated to form an axial rod‐like inclusion, and the other with large, spherical, uniformly electron‐dense granules. Correlation of light and electron microscope observations indicated that the neutrophilic granulocytes with weakly basophilic, elongated granules become weakly eosinophilic, as eosinophilic granulocytes, and these in turn develop to eosinophils with granules containing axial rods. The other granulocyte type forms another population of eosinophils with spherical granules.The inter‐relationship of these granulocytes, the identification of eosinophilic granulocytes, or heterophils, as immature eosinophils, and the co‐existence of two morphologically distinct eosinophil forms are discussed.