What is "hingemouth"

The hingemouth (Phractolaemus ansorgii) is a small freshwater fish that is found only in west central Africa, the sole member of the family Phractolaemidae.

The mouth can extend like a small trunk, thus the name, and has just two teeth, both in the lower jaw. The swim bladder has two compartments, and can function as a lung, allowing the hingemouth to survive in oxygen-poor environments.