Accumulation of radiocalcium from the aquatic medium via the cloaca and bucco-pharynx of Australian freshwater turtles (Chelidae).

1. The cloacal and bucco-pharyngeal regions of three species of Australian freshwater turtles were experimentally compared for their ability to take up radiocalcium directly from the aquatic medium. 2. The cloacal route was at least 4 times more important than the bucco-pharyngeal route for radiocalcium uptake, in each of the three species investigated. 3. Histological examination of anatomical regions in the cloaca showed that the cloacal bursae of three species (E. dentata, C. longicollis and E. signata) had abundant villi and infolded mucosal epithelia that increase the surface area of the epithelium exposed to the aquatic medium. 4. Electron microscopic studies on the mucosal epithelium of the cloacal bursae showed that it contained many structural characteristics indicative of an exchange function and consistent with the cloacal bursae being an important site of radiocalcium uptake within the cloaca.