Many species also possess photophores (bioluminescent organs) which may be located on either the body, the tentacular clubs, the surface of the eye, or the eyelid. These photophores have a "lens" of chromatophores, pigment cells which may allow the squid to modify the colour of the light produced by the photophores. The mantle of some species is adorned with conical or hemispherical tubercles. The arm suckers possess sharp or blunt conical teeth, which are either larger or present only on the distal side. Coloration is typically a rich reddish brown.
Members of this family have scarcely been observed in life, but at least two species (Idioteuthis hjorti and Mastigoteuthis magna) are known to hover above the ocean bottom in a vertical orientation, the head pointing downward. The squid use their large fins to maintain this orientation and use both their extended tentacles as a pair of snares, held rigidly at a constant distance apart: this has been termed the "tuning fork" position. Prey items apparently consist primarily of benthic crustaceans.
Although mastigoteuthids possess ink sacs (which would suggest forays into shallower, lit waters), all observations have been over the bottom in deep water. The squid seem to lack the ability of rapid jet propulsion and instead rely on their capable fins.
The question mark (?) indicates questionable placement within the genus. The specific arrangement of the species under Idioteuthis indicates 4 different subgroups under revision. I. famelica is now verified to be member of genus Mastigoteuthis.