Q: While chunking at night during our mid-September trip near the Atlantis Canyon south of Rhode Island, we saw this thing swim up into the lights. My buddies thought it was a cuttlefish, but after dipping it up, I'm guessing it's some sort of nautilus. When I put it in the bucket, it started jetting around in circles and banging into the bucket's sides, so my buddies convinced me to release it. The cool thing was the membrane on the outside of the shell: It changed colors when touched, like a cuttlefish.

Capt. Bob Frevert
Jupiter, Florida

A: That's a neat catch, Bob! You captured and released an argo-naut, also known as a paper nautilus. Argonauts are small octopuses that live in the water column rather than on the seafloor like most other octopuses. The shell-like structures surrounding argonauts are actually egg cases; based on the size, shape, color and texture of the egg case belonging to the argonaut you captured, your specimen appears to be a female Argonauta argo. While males of this species attain a maximum mantle length of less than an inch, females' mantles may reach four inches, with egg cases more than a foot in length. Argonauts have the bility to dispatch prey by injecting them with venom produced by salivary glands; the venom enters wounds created by the argonauts' parrotlike beaks. As is also the case in other cephalopods, chromatophores, or pigment cells, in an argonaut's skin are attached to muscles under direct neurological control, which gives these animals the ability to undergo extremely rapid color changes such as you observed. Only occasionally do I find the fragile egg cases inside the stomachs of dolphin (mahi). — Ray Waldner