Saccopharyngiformes is an order of unusual ray-finned fish superficially similar to eels, but with many internal differences. Most of the fish in this order are deep-sea types known from only a handful of specimens such as the Umbrella Mouth Gulper Eel. Saccopharyngiformes are also bioluminescent in several species. Some, such as the swallowers, can live as deep as 10,000 feet (3,000 m) in the ocean, well into the aphotic zone.
