cephalopod fin
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Cephalopod fins, sometimes known as wings,Young, R.E., M. Vecchione & K.M. Mangold (1999). [http://tolweb.org/accessory/Cephalopoda_Glossary?acc_id=587 Cephalopoda Glossary]. Tree of Life Web Project. are paired flap-like locomotory appendages. They are found in ten-limbed cephalopods (including squid, bobtail squid, cuttlefish, and Spirula) as well as in the eight-limbed cirrate octopuses and vampire squid. Many extinct cephalopod groups also possessed fins. Nautiluses and the more familiar incirrate octopuses 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. {{doi|10.2989/025776198784126340}}
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). [http://tolweb.org/accessory/Cephalopoda_Fin_Cartilage?acc_id=1969 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). [http://tolweb.org/accessory/Cephalopod_Fin_Attachment?acc_id=1974 Cephalopod Fin Attachment]. Tree of Life Web Project.
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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 paralarval chiroteuthids)Vecchione, M., B.H. Robison & C.F.E. Roper (1992). {{cite web|url= http://si-pddr.si.edu/jspui/bitstream/10088/11044/1/iz_Vecchione-1992.pdf |title=A tale of two species: tail morphology in paralarval Chiroteuthis. }} 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). {{cite web |url= http://www.geo.fu-berlin.de/geol/fachrichtungen/pal/eigenproduktion/Band_03/10.pdf |title= Two pairs of fins in the late Jurassic coleoid Trachyteuthis from southern Germany. |access-date= 2012-12-22 |archive-url= https://web.archive.org/web/20170812044527/http://www.geo.fu-berlin.de/geol/fachrichtungen/pal/eigenproduktion/Band_03/10.pdf |archive-date= 2017-08-12 |url-status= dead }} Berliner Paläobiologische Abhandlungen 3: 91–99.
File:Grimalditeuthis bonplandi (rotated).jpg with "secondary fins" supported on a well-developed tail]]
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). [http://tolweb.org/accessory/Cephalopod_Fin_Length?acc_id=2055 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). [http://tolweb.org/accessory/Cephalopod_Fin_Position?acc_id=2041 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). [http://tolweb.org/accessory/Decapodiform_Fin_Shapes?acc_id=2029 Decapodiform Fin Shapes]. Tree of Life Web Project.
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| File:Onychoteuthis banksii1.jpg |Ventral (left) and dorsal aspects of Onychoteuthis banksii, showing classic sagittate fins
| File:Thysanoteuthis rhombus (Naef).jpg |The diamondback squid, Thysanoteuthis rhombus, has full-length rhomboid fins
| File:Mastigoteuthis magna.jpg |Mastigoteuthis magna has very large circular fins, characteristic of its family, Mastigoteuthidae
| File:Galiteuthis phyllura.jpg|Galiteuthis phyllura in dorsal (top) and ventral views, showing its lanceolate fins
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| File:Spirula spirula1.jpg |Spirula spirula has small ear-shaped fins on either side of a terminal photophore
| File:Chtenopteryx sicula 1.jpg |The highly distinctive ribbed fins of Chtenopteryx sicula
| File:Sepia officinalis1.jpg |Skirt-like fins spanning the length of the mantle are characteristic of sepiids, such as this Sepia officinalis
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