Whip-lash squid

The Mastigoteuthidae, also known as whip-lash squid, are a family of small deep-sea squid. Approximately 20 known species in two genera are represented, with members found in both the mesopelagic and bathypelagic zone of most oceans. They are sometimes treated as a subfamily (Mastigoteuthinae) of the Chiroteuthidae, which are also called whip-lash squid on occasion.

Description
Most mastigoteuthids are rather small, from 3–15 centimetres total mantle length. Their most distinctive features are their extremely elongate tentacles&mdash;which retract into membranous lateral sheaths of the fourth (and largest) arms&mdash;and their very large ovate fins, which may occupy up to 80% of the mantle length in some species. Unlike most other squid, the club of the mastigoteuthid tentacle is not significantly (usually not at all) broader than the rest of the tentacle and is covered in very small suckers&mdash;in some species, invisible to the naked eye&mdash;which impart an extremely sticky property to the clubs, themselves answering for 70% or more of the tentacle's length in some species.

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.

Two species (Idioteuthis tyroi and I. cordiformis) are known to have greatly expanded tentacular clubs as paralarvae and subadults.

Behaviour
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.

Species

 * Genus Idioteuthis
 * Idioteuthis cordiformis
 * Idioteuthis danae
 * Idioteuthis famelica
 * Idioteuthis hjorti
 * Idioteuthis latipinna
 * Idioteuthis okutanii
 * Idioteuthis tyroi
 * Genus Mastigoteuthis
 * Mastigoteuthis agassizii
 * Mastigoteuthis atlantica
 * Mastigoteuthis dentata
 * ? Mastigoteuthis flammea
 * Mastigoteuthis glaukopsis
 * Mastigoteuthis grimaldii
 * Mastigoteuthis inermis
 * Mastigoteuthis magna
 * Mastigoteuthis psychrophila
 * Mastigoteuthis pyrodes
 * ? Mastigoteuthis schmidti

The question mark (?) indicates questionable placement within the genus.