Bigfin squids are a group of rarely seen cephalopods with a distinctive morphology. They are placed in the genus Magnapinna and family Magnapinnidae. Although the family was described only from larval, paralarval, and juvenile specimens, numerous video observations of much larger squid with similar morphology are assumed to be adult specimens of the same family.
The arms and tentacles of the squid are both extremely long, estimated at . These appendages are held perpendicular to the body, creating "elbows". How the squid feeds is yet to be discovered.
Magnapinna is thought to be the deepest-occurring squid genus, with sightings as deep as below the surface, making it the only squid known to inhabit the hadal zone.
Taxonomy
Magnapinna is the sister group to Joubiniteuthis, another little-known deep-sea squid with an unusual body plan and long arms. Both Magnapinna and Joubiniteuthis are monotypic genera within their own families, Magnapinnidae and Joubiniteuthidae, respectively. They are also closely related to the "whip-lash squid" in the families Chiroteuthidae and Mastigoteuthidae.'
Physical specimens
The first record of this family comes from a specimen (Magnapinna talismani) caught off the Azores on 10 August 1883. Due to the damaged nature of the find, little information could be discerned, and it was classified as a mastigoteuthid, first as Chiroteuthopsis talismani
left|thumb|A juvenile [[Magnapinna talismani, the first known species from the family, with damaged arms]]
During the 1980s, two additional immature specimens were found in the Atlantic (Magnapinna sp. A), and three more were found in the Pacific (Magnapinna pacifica). Researchers Michael Vecchione and Richard Young were the chief investigators of the finds, and they eventually linked them to the two previous specimens, erecting the family Magnapinnidae in 1998, with Magnapinna pacifica as the type species.
Sightings
The presumed adult stage of Magnapinna is known only from video observations from submersibles, deep sea oil rig cameras, and remotely-operated vehicles (ROVs); no physical specimens have yet been collected, leaving their exact identity unknown. These individuals and the collected juvenile specimens share the large fins and the vermiform arm tips with no suckers, but the iconic elongated arm tips are known only from the presumed adult individuals. Although it has not been directly confirmed whether these squid are the same as the Magnapinna known from specimens, it is largely accepted that they are members of Magnapinnidae.
Although observations had been made over a decade earlier, adult bigfin squid only became known to science in 2001, when marine biology student Heather Holston sent footage of what she described as a "21-foot-long squid" to teuthologist Michael Vecchione. The footage had been recorded from an ROV in the Gulf of Mexico in January 2000 at the request of Holston's boyfriend Eric Leveton, who planned on showing it to her. Leveton was a structural engineer aboard the oil-drilling ship Millennium Explorer, who had happened to look into the ROV operation shack when the squid was observed by operators. Although Vecchione initially surmised from Holston's description that the footage might be the first video of a live giant squid (Architeuthis dux), he realized that the video itself portrayed a completely different squid that had no known identity.