It is found in cold, high latitude waters of the North Pacific where it is among the most numerous squid species recorded.

The cylindrical bodies of magister armhook squid are muscular with very soft reddish brown skin.

The clubs at the end of both tentacles are covered in 20 rows of suckers; these are smaller in B. magister nipponensis.

The wing-like fins at the rear of the body are rather large and may reach up to 50 percent of the mantle length.

Other predators include seabirds, northern fur seals, grenadiers, halibut and several species of salmon.