Light and electron microscopy of the carotid body of the Weddell seal shows two types of cells, the main and the sustentacular cells.

The main cells contain dense osmiophilic granules in variable amount. Their cytoplasma shows either a high or a low electron density. On this basis light and dark main cells were distinguished.

The differences in cytoplasm electron density and the great variability in the number of granules were interpreted as expressions of different stages in a process of secretory nature.

A very rich innervation with outstanding nerve endings was observed in the carotid body of the Weddell seal. This picture is similar to that observed in stimulated carotid bodies. The carotid body of the Weddell seal a marine mammal that stays underwater for a long stretch of time, may be considered as subjected to frequent stimulations.