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 is known only from larval, paralarval, and juvenile specimens, some authorities believe adult specimens have also been seen. Several videos have been taken of animals nicknamed the "long-arm squid", which appear to have a similar morphology. Since none of the seemingly adult specimens has ever been captured or sampled, it remains uncertain if they are of the same genus or only distant relatives.
The arms and tentacles of the squid are both extremely long and believed to be 4 to 8 m (13 to 26 ft) long. These appendages are held perpendicular to the body, creating "elbows". How the squid feeds is yet to be discovered.