The Paper Nautilus (Argonauta argo)

Class: Cephalopoda
Subclass: Coleoidea
Superorder: Octopodiformes
Order: Octopoda
Suborder: Incirrina
Tribus: Argonautida
Family: Argonautidae
 

Paper Nautilus (Argonauta argo). Picture: Bernd Hofmann, Wikipedia.

One of the most astounding cephalopods is the paper nautilus also known as argonaut. 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.

Immature male argonaut. Picture: Chung 1910.

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.

Generally living argonauts are difficult to find, possibly because of their pelagic way of life. Much more often their shells, sometimes, masses of them, are deposed on the shore by the sea. That way they also find their way into collectors' packs.

The scientific name of the paper nautilus, especially the largest species, Argonauta argo, is of mythical Greek origin. The argonauts were a group of Greek heroes that, led by Iason, travelled to Kolchis to gain the golden fleece. The were called that way, because their ship was the Argo. In Greek argonaut means "who travels on the Argo". The argonaut's discoverers probably mistook its sail-like flaps as a locomotive organ and thus drew the similarity to the mythical Argo.