The only vaguely suitable turtles would be softshells, and your setup would likely be less than ideal (they prefer to be able to reach the water's surface - via extensile neck and tubular nostril extensions - whilst lying on the substrate), and might wish to utilize (albeit quite infrequently) a haul-out platform (above which should be a herpetile spot light for purposes of basking); vitamin supplements and
UV lights would probably be necessary as well. In addition, the females of most North American
Trionyx spp. (the genus most frequently available in the aquarium hobby) attain carapace lengths nearing two feet, at which point they are more than capable of severing fingers (the males of most morphotypes are more manageable as regards length); certain Eurasian and African species (more infrequently available) may achieve carapace lengths exceeding four feet.
The only truly aquatic snakes I know of are
tentacle snakes (Erpeton tentaculatum) (a rear-fanged, and though quite reluctant to bite, mildly venomous Southeast Asian Colubrid).
E. tentaculatum is often imported highly stressed and with a substantial parasite load, but hobbyists have reported their specimens to thrive in captivity, feeding well and, in some cases, breeding.
Of the following - aquatic invertebrates (from shrimp to sponges and diving beetles); salamanders; caecilians; and frogs - what exactly interests you?
