The Blood Cell Morphology of the Harbor Seal, Phoca vitulina Linnaeus, 1758, from the Commander Islands

—Blood cells of harbor seals, Phoca vitulina Linnaeus, 1758, from the Commander Islands population have been characterized in detail for the first time. Data on the composition, size, and ratio of red blood cells (RBCs), white blood cells (WBCs), and platelets in the peripheral blood of immature and mature seals are provided. A micrograph library for all types of peripheral blood cells of harbor seal is presented. The blood cell morphology of this seal generally corresponds to that of other pinniped species; however, neutrophils with Döhle bodies, reactive lymphocytes, and hypersegmented neutrophils have been found in blood films. Increased numbers of eosinophils (10–25%) have been recorded from the WBC differential counts of all examined seals. Mature seals had higher numbers of eosinophils (p = 0.04) and large lymphocytes (p = 0.005); immature seals had higher numbers of monocytes (p = 0.04) and Howell–Jolly bodies in RBCs (p = 0.03). Microfilariae and nucleated RBCs were observed in blood films of two mature seals.