The Gonatus Onyx is in the class Cephalopoda, in the phylum Mollusca. It is also known as the Clawed arm hook squid or Black-eyed squid. It got these names from the characteristic black eye and from its two arms with clawed hooks on the end that extend a bit further than the other arms. 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 mantle size of the Gonatus Onyx has been known to reach up to 18cm. G. Onyx size varies from region to region, with larger members of the species being found in warmer areas.
The type specimen was collected off California and is deposited at the Santa Barbara Museum of Natural History.
The Gonatus Onyx or Black-eyed squid is a relatively smaller-sized squid with an average mantle length of about 12 cm, with some warmer water individuals reaching up to 18 cm. This species shows sexual dimorphism in mantle size with females maturing faster and growing a couple of cm larger than the males. The mantle makes up a majority of their body length, the arms make up another about 40mm on average. They have characteristic black eyes on either side of their head, these highly developed sensory organs are helpful for hunting in pitch black conditions. The armature consists of five pairs, one pair with a large primary hook at the end and multiple rows of suckers, the other four pairs are generally shorter and do not have this tentacular hook, still lined with rows of suckers. The use of clawed arms are thought to be used in hunting and for better catching and handling of their prey. Some individuals are harder to identify as the tentacular club is very fragile and easily damaged. The mantle’s fins are smaller than the other members of Gonatids and the tail is less tapered. G. Onyx like most squid move using a propulsive force, using water expelled from a siphon with the combination of fin movements. The juvenile G. Onyx has been observed using ink as a defensive mechanism and as a propulsive force, while the adults rarely use ink and rather choose to use a faster propulsive force. Matured members possess chromatophores, specialized small organs under the skin of the squid, which are used to change colors to hide reflective internal organs. They have a beak, like all cephalopods; it is relatively small compared to other species. The upper part of the beak is sharp and has less curvature, while the bottom is curved, duller, and shorter. This specialized beak makes it easier for squid to attack prey larger than themselves.
G. Onyx is a very common cephalopod that is found in the Northern Pacific Ocean, ranging from coastal California to the east coast of Japan, and are found as far north as the Bearing Sea. The adults and juveniles inhabit different areas, with the more solitary adults tending to like deeper water and the pack hunting juveniles preferring shallow coastal waters. They have one of the lowest seasonal variations over wide areas from the members of the family Gonatidae. The depth distribution is bimodal and follows a certain diel rhythm. During the day they tend to stay at deeper depths with adults found from 400-1000m, with an average depth of around 700m. Younger members are found at 0-800m during the day with an average of around 400m. During the night both adults and juveniles tend to rise from the deeper water. Adults at night have a range of depths from 100-800m with a large majority found around 400-500m. Juveniles have a smaller range from 0-500m and are more evenly spread out with most found from 0-300m.
