see text The Hexanchiformes /hɛkˈsæŋkɪfɔːrmiːz/ are a primitive order of sharks,[a] numbering just seven extant species in two families.

Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens.

However, more recent phylogenetic studies indicate that while primitive, they in fact belong to the superorder Squalomorphii, which also contains dogfishes, angelsharks, and sawsharks, although they are thought to be the most basal member of the group.

However, genetic studies have found them to be each others' closest relatives, and they share certain derived features supporting them both being in the same order.

They are most common in cold deep water in the tropics, but are also found closer to the shore in more temperate regions.