each with two tubes whose frontal openings lie close to the upper jaw, and the posterior openings further behind near the eyes. A 395-million-year-old fossil lobe-finned fish called Kenichthys campbelli has something between a choana and the external nostrils seen on other fish. The posterior opening of the external nostrils has migrated into the mouth. In lungfish, the inner nostrils are regarded as an example of parallel evolution. The fossil lungfish Diabolepis shows an intermediate stage between posterior and interior nostril and supports the independent origin of internal nostrils in the lungfish. Hagfishes have a single internal nostril that opens inside the mouth cavity, while chimaeras have open canals that leads water from their external nostrils into their mouths and through their gills. References Skull