Composition and ultrastructure of elasmobranch granulocytes. III. Sharks (Lamniformes)

The peripheral blood granulocyte composition of five species of shark is given together with ultrastructural observations made on the epigonal organ and blood of Mustelus lenticulatus and spleen of Apristurus sp. Three granulocyte lineages occurred in Mustelus . Ultrastructurally, eosinophilic granulocytes contained granules that were very variable in size and contained parallel fibrillar arrays that were unidirectional in small granules, but which were often orientated in several directions in larger granules. This dense core material sometimes formed angular crystalloids.
Eosinophils had ovoid or irregular granules that were usually uniformly electron-dense, but some had an eccentric ovoid area of greater electron-density. Some eosinophils enter the blood where they are phagocytic, but others, in blood and epigonal organ, showed an unusual but characteristic process of disintegration, leaving a ragged cell full of cellular debris.
The third granulocyte type had features of mast cells and basophils of higher vertebrates and was tentatively identified as belonging to that lineage. The inter-relationships of these cells, and of them with granulocytes of other elasmobranchs, are discussed.