The anatomy of the gills of aquatic gastropods has not been extensively studied, and in particular, there are few recent studies that contain ultramicroscopic images. Similarly, the literature on the anatomy of the lungs of air-breathing terrestrial snails is not voluminous. Apple snails of the genus Pomacea possess both a gill and a fully functional lung. The lung is used to breathe air and as a flotation device. This study reports on the anatomy of the gill, lung, and pneumostome of the invasive species Pomacea maculata. The gill has a structure similar to that reported in other gastropods. The gill is monopectinate and consists of numerous triangular filaments. Ciliary tracts populate the distal portions of the filaments. The filaments are primarily connective tissue, interspersed with abundant muscle bands and hemolymph sinuses. The lung is a large ovoid sac; the floor is attached to the foot of the snail and the roof of the lung underlies the mantle epithelium. The lung tissue layers consist of connective tissue and smooth muscle bundles, and hemolymph spaces are present in both the floor and roof. Cells that contain calcium granules are very abundant in the lung tissue. Patches of cilia adorn the epithelium adjacent to the central airspace. The pneumostome is a muscular structure and is heavily ciliated. The lung volume of a 50-g animal is about 6 mL. The results of this study add to the knowledge of the anatomy of respiratory organs in molluscs and show that the lung is a major site of storage of calcium.