Saccopharyngiformes is an order of unusual ray-finned fish, superficially similar to eels, but with multiple internal differences. Most of the fish in this order are deep-sea types known from only a handful of specimens, such as the pelican eel. Some species are bioluminescent. Some, such as the "swallowers", can live as deep as 3,000 m (10,000 feet) in the ocean, well into the aphotic zone. Saccopharyngiformes were found by deep sea fishermen's nets. Extensive research has not been conducted on them due to being indirectly observed.