Podocnemis unifilis is the most abundant semi-aquatic turtle species within the Podocnemis genus, capable of reaching up to 50 cm in length and weighing up to 12.5 kg. Cloacal bursae are organs in the urogenital system of semi-aquatic turtles, used for gas exchange, buoyancy control, and ionic exchange. Lungs, on the other hand, are part of the respiratory system and are utilized for gas exchange. The aim of this study was to describe the morphological and histological aspects of the cloacal bursae and lungs. Specimens were collected from the Tocantins and Javaés rivers in the state of Tocantins, Brazil, using hook-and-line fishing and 'pulo' technique. After collection, biometrics were taken, and euthanasia was performed. During euthanasia, the cloacal bursae and lungs were removed and fixed in buffered formalin for 72 hours. Following fixation, they were stored in 70% alcohol in containers until paraffin embedding, microtomy, and Hematoxylin and Eosin staining for light microscopy analysis. For scanning electron microscopy of the cloacal bursae, the material was washed after fixation, stored in a 1000 μL 16% glycerol solution for 24 hours. Samples were dehydrated and dried in a critical point chamber, attached to 'stubs,' and gold-coated. In the cloacal bursae, four layers were observed: mucosa, submucosa, muscular, and serosa, featuring a simple columnar epithelium on the lamina propria, the presence of blood vessels and capillaries, and smooth muscle tissue. In the lungs, there were projections forming chambers, an epithelium with cilia and goblet cells. This organ showed a significant number of blood vessels and capillaries, mucosal and muscular layers, and the presence of hyaline cartilage. In conclusion, the cloacal bursae are relevant for gas exchange, although the lungs are more efficient. This is due to the presence of a higher number of capillaries beneath the epithelium and a greater number of mucus-secreting cells. Additionally, the cloacal bursae are unique accessory organs that can differentiate among species and serve various functions beyond gas exchange.
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