A transparent barrel-bodied squid whose eyes and gut are often all a torch beam picks up.
A clear rounded or bottle-shaped mantle with a pair of large eyes and a compact opaque gut suspended inside it, arms usually held together in a short bunch. Most of the animal is invisible, so what the beam returns is two eyes and a dark package hanging in nothing. Juvenile squid of several other families are also transparent, and this entry is pitched at the family because a photograph will not normally settle which cranchiid it is.
The transparency has a mechanism. Cranchiids carry a large fluid-filled coelomic chamber holding ammonium chloride, which is lighter than seawater and gives the animal near-neutral buoyancy without a swim bladder or continuous swimming. The same chamber makes up most of the body volume and is optically clear. The gut is held vertically in many species so that it presents the smallest possible silhouette to anything looking up from below, and some species carry photophores beneath the eyes to cancel their own shadow against the surface light.
Adults live deep and are rarely met. What comes up on a blackwater dive is almost always a juvenile, and juveniles of some genera look nothing like the adult — long eye stalks and a drawn-out neck that shorten as the animal grows. They are easily disturbed and will jet away from a hard focus light, so a wide beam held slightly off the animal usually buys more time.
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.
