Image taken at Blairgowrie Marina of this amazing Cephlapod, a very rare find, the first one I have ever seen alive in 7 years of diving. They often come into shallow waters to end their life cycle & allow their eggs to disperse.
This (super-)family of octopus-like cephalopods lives in pelagic habitats of the subtropics and tropics. Pelagic habitats are those of the free ocean water away from the bottom, especially at the water surface.
Though the argonaut is called paper nautilus, it is neither made from paper nor is it a nautilus. It not even is closely related to the nautilus, though both are cephalopods.
The argonaut’s shell is special among all molluscs. It is only built by the female, and only as case for the protection of the argonaut’s eggs, that are placed inside in long threads. The female argonaut lives in the shell’s entry and guards the eggs, until the young hatch. At the ends of the first tentacle pair the argonaut (argonauts like other octopus relatives have eight tentacles) has got wide sail-like flaps. Usually the female argonaut holds these flaps spread over the shell, but they also serve it to catch prey that swims into them.
The male argonaut is much smaller than the female. While the latter reaches a size of up to ten centimetres, the shell being up to 45 centimetres large, the male only reaches less than 2 centimetres size. The male argonaut is special because of its altered third tentacle, that is kept in a pouch until it is needed. Like among other cephalopods this tentacle is called the hectocotylus. The male argonaut, other than its larger relatives, often leaves its hectocotylus behind, the latter finding the target on its own. It seems obvious that the male argonaut dies after copulation, as no argonauts with their hectocotyli grown back have been found so far.