It is a squid in the family Gonatidae, found most commonly in the northern Pacific Ocean from Japan to California.

They are one of the most abundant cephalopods off the coast of California, mostly found at deeper depths, rising during the day most likely to feed.

The type specimen was collected off the coast of California and was deposited at the Santa Barbara Museum of Natural History.

This species shows sexual dimorphism in mantle size with females maturing faster and growing a couple of centimeters larger than the males.

G. onyx like most squid move using a propulsive force, using water expelled from a siphon with the combination of fin movements.

The upper part of the beak is sharp and has less curvature, while the bottom is curved, duller, and shorter.

Females lay their eggs from April to July, brooding them for about six to nine months until the hatchlings are ready to emerge in depths exceeding 2,500 m (8,200 ft).

[9] These juveniles possess the ability to embark on extensive vertical migrations towards shallower waters abundant in nutrients.

[9] Once the egg masses are laid, females migrate to deep waters, a strategic move to evade potential predators.

[8] Encased within a black jelly-like substance, the eggs reside in individual chambers connected by a delicate membrane.

Hatchlings mature into juveniles in about 3 months and are very active schooling predators during this time, they develop their hooks on arms and tentacles.

Juveniles quickly accumulate lipids to prepare for reproduction, however, the exact reason for schooling is unknown.

Cannibalism could have evolved as a way to limit reproductive competition or as a result of low food availability in the deep waters.

They release ink in long rope-like shapes that allow the squid to be mistaken as a different animal by predators so they can plan their escape.

[13] Adults do not exhibit the fast defense behaviors seen in juveniles because they have less predation in the deeper waters and it requires more energy consumption which is a limited resource in the deep.