Cephalopod fins, sometimes known as
wings,
[Young, R.E., M. Vecchione & K.M. Mangold (1999). Cephalopoda Glossary. Tree of Life Web Project.] are paired
fin. They are found in
Decapodiformes (including
squid,
bobtail squid,
cuttlefish, and
Spirula) as well as in the
Octopodiformes Cirrina and
vampire squid. Many extinct cephalopod groups also possessed fins.
and the more familiar
Incirrina lack swimming fins. An extreme development of the cephalopod fin is seen in the
bigfin squid of the family
Magnapinnidae.
[Vecchione, M. & R.E. Young (1998). The Magnapinnidae, a newly discovered family of oceanic squid (Cephalopoda: Oegopsida). South African Journal of Marine Science 20(1): 429–437. ]
Fins project from the mantle and are often positioned dorsally. In most cephalopods, the fins are restricted to the posterior end of the mantle, but in cuttlefish and some squid they span the mantle's entire length.
Fin attachment varies greatly among cephalopods, though in all cases it involves specialised fin cartilage (which reaches its greatest development in Octopodiformes).[Young, R.E., M. Vecchione & K.M. Mangold (2000). Cephalopoda Fin Cartilage. Tree of Life Web Project.] A fin may be attached to the internal shell or shell remnant (such as the gladius), to the opposite fin, to the mantle, or a combination of these.[Young, R.E., M. Vecchione & K.M. Mangold (2001). Cephalopod Fin Attachment. Tree of Life Web Project.]
Tail and secondary fins
Certain squid species possess a
tail, which is an extension of the body past the fins.
The tail may be said to start at "the point where a hypothetical line, continuous with the broad posterior edge of the fin, crosses the midline of the body".
This tail may be lost with age (as in most
Chiroteuthidae)
[Vecchione, M., B.H. Robison & C.F.E. Roper (1992). Proceedings of the Biological Society of Washington 105(4): 683–692.] or remain through
sexual maturity (as in
Grimalditeuthis).
Grimalditeuthis and larval
Chiroteuthis are unusual in that they possess a pair of
flotation devices or "secondary fins" attached to the tail. The
vampire squid (
Vampyroteuthis infernalis) also has two pairs of fins during a brief period of its
ontogeny, and secondary fins have been reported in the extinct
Trachyteuthis.
[Donovan, D.T., L.A. Doguzhaeva & H. Mutvei (2003). Berliner Paläobiologische Abhandlungen 3: 91–99.]
Fin morphology and placement
Cephalopod fin morphology is highly variable. The fins may be large and muscular, extending for the entire length of the mantle, or greatly reduced (sometimes less than 10% ML) and restricted to the mantle's posterior end.
[Young, R.E., M. Vecchione & K.M. Mangold (2001). Cephalopod Fin Length. Tree of Life Web Project.] Fin placement in cephalopods is often termed
normal,
terminal, or
subterminal, depending on their position with respect to the muscular mantle.
[Young, R.E., M. Vecchione & K.M. Mangold (2001). Cephalopod Fin Position. Tree of Life Web Project.]
Eight major fin shapes can be distinguished among the Decapodiformes: sagittate (the most common shape in squid), rhomboid, circular/elliptical, lanceolate, ear-shaped, ribbed, lobate, and skirt-like.[Young, R.E., M. Vecchione & K.M. Mangold (2001). Decapodiform Fin Shapes. Tree of Life Web Project.]
