[5][6] Magnapinna is the sister group to Joubiniteuthis, another little-known deep-sea squid with an unusual body plan and long arms.

Researchers Michael Vecchione and Richard Young were the chief investigators of the finds, and eventually linked them to the two previous specimens, erecting the family Magnapinnidae in 1998, with Magnapinna pacifica as the type species.

[12] The presumed adult stage of Magnapinna is known only from video observations from submersibles and remotely-operated vehicles (ROVs); no physical specimens have yet been collected, leaving their exact identity unknown.

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.

Analysis by Vecchione et al of previous footage from submersibles found other video records of bigfin squid, the earliest from 1988.

[18][15][19] Independent of Vecchione's publication, Guerra et al published a paper the following year analyzing some of the early bigfin squid footage, and also identified them as potential adult magnapinnids.

[22] Viewing close-ups of the body and head, it is apparent that the fins are extremely large, being proportionately nearly as big as those of bigfin squid larvae.

While their exact identity is unknown, all of the discovered specimens can be observed to have a brown-orange color body, translucent fins, near-white tentacles, and dark eyes.

Scientists have speculated that the bigfin squid feeds by dragging their arms and tentacles along the seafloor and grabbing edible organisms from the floor.

By comparison with the visible parts of the ROV, the squid was estimated to measure 7 metres (23 ft) with arms fully extended.

[20] The Nautile filmed another Indian Ocean specimen at 19°32′S 65°52′E / 19.533°S 65.867°E / -19.533; 65.867 (Bigfin squid (sighting 2000, Atalante)) and 2,576 metres (8,451 ft), in the area of Rodrigues Island, in May 2000.

In May 2001, approximately ten minutes of crisp footage of a bigfin squid were acquired by ROV Tiburon, causing a flurry of attention when released.

[18][20] On 11 November 2007, a bigfin squid was filmed off Perdido, a drilling-site owned by Shell Oil Company, located 200 statute miles or 320 km off Houston, Texas in the Gulf of Mexico.

[24][28][29] Observations of bigfin squid were made in the Great Australian Bight during towed camera and remote operated vehicle surveys in 2015 and 2017 respectively.

[30] In March 2021, during the expedition to document the wreck of the USS Johnston, the submersible DSV Limiting Factor recorded footage of a juvenile bigfin squid from the Philippine Trench at a depth of 6,212 metres (20,381 ft).

[5][6] On 9 November 2021, a video of a bigfin squid was captured at a ridge feature off the West Florida Escarpment by an ROV from the NOAAS Okeanos Explorer as part of the Windows to the Deep 2021 expedition.