Histology of selected tissues of the leopard seal and implications for functional adaptations to an aquatic lifestyle.

The microscopic anatomy of the cardio-respiratory system, digestive system, kidney, lymphatic system and integument was investigated in the leopard seal, Hydrurga leptonyx, by examining histological sections of tissues collected from leopard seals in Antarctica and New South Wales, Australia. The majority of the tissues had similar histological features to those described in terrestrial mammals and other pinniped species, particularly phocid seals. Differences noted included readily identifiable Purkinje cells within the endocardium, muscular rather than cartilaginous reinforcement of the smaller airways, a single capillary layer within the alveolar septa, limited and variable keratinization of the oesophageal epithelium, few lymphoid follicles within the lamina propria of the gastrointestinal tract, and an absence of a sporta perimedullaris musculosa described in the kidney of cetaceans and some pinniped species. Adaptations of the lung, spleen and integument, similar to those described in other pinnipeds, including reinforcement of the pulmonary terminal airways, prominent pulmonary interlobular septa, ample smooth muscle in the capsule and trabeculae of the spleen, increased thickness of the epidermis, well-developed dermal sebaceous glands, and a thick blubber layer, appear to confer upon the leopard seal advantages related to its aquatic lifestyle.