They are found worldwide, from northern to tropical waters, and from shallow coastal seas to the open ocean.

[2] All members of the family Etmoperidae and Dalatiidae and Zameus squamulosus possess photophores, luminous organs, and exhibit intrinsic bioluminescence.

[3][4] The common ancestor of Dalatiidae, Etmopteridae, Somniosidae, and Oxynotidae possessed a luminous organ and used bioluminescence for camouflage by counterillumination.

[5] Etmopteridae possess more complex photophores [7] and utilize bioluminescence for ventral counter illumination as well as species recognition.

[8] Many squaliforms have a spine in front of each of the two dorsal fins, likely a trait of the common ancestor of this clade.