A deep-water squid whose young rise into the top of the water column at night.
The only species in its family. Adults reach about 25 cm in the mantle and live in the mesopelagic zone, several hundred metres down by day; what a blackwater diver photographs is a juvenile a few centimetres long, transparent, with orange-red chromatophores scattered over the mantle and head, large silvered eyes and long slender arms. The generic name refers to the hooks that replace some of the arm suckers in adults, which are not developed at this size.
It carries light organs on the underside of the body and around the eyes, used for counter-illumination — matching the faint light from above so that the animal casts no silhouette to anything looking up at it. Like most of the mesopelagic fauna it takes part in the nightly vertical migration, which is what puts it within reach of a diver behind a lit downline. Records from blackwater dives here are of juveniles, and identification of small squid on a blackwater dive is frequently provisional: several unrelated families produce transparent, orange-spotted young of a similar size.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
