The Saccopharyngiformes are a derived lineage of unusual eels within the order Anguilliformes, and includes families Cyematidae, Monognathidae, Eurypharyngidae, Saccopharyngidae, and the proposed family Neocyematidae. Most of the fish in this group are deep-dwelling and rarely seen, typically known from only a handful of specimens. Species include recognizable fish such as pelican eels (also commonly known as gulper eels) and bobtail eels. Some can live deep in the ocean, well into the aphotic zone, approximately deep. Extensive research has not been conducted on them due to being indirectly observed, with some species known only from their larvae.
The three established families of the suborder Saccopharyngoidei (Eupharyngidae, Monognathidae, Saccopharyngidae) all exhibit sexual dimorphism.
Taxonomy
Until recently,<!--What year?--> the order "Saccopharyngiformes" was accepted as a separate order from Anguilliformes, based on their distinct morphological differences from the rest of the "true eels". Genetic work over the past few years<!--Specify the year numbers--> has shown that it is instead a derived lineage within the Anguilliformes.
The four (proposed five) families in two suborders are:
- Suborder Cyematoidei
- Cyematidae (bobtail snipe eels)
- Suborder Saccopharyngoidei
- Eurypharyngidae (gulpers)
- Monognathidae (one-jaws)
- Saccopharyngidae (swallowers)
- Neocyematidae (proposed)