Argonaut (animal)

Argonaut (animal)

The argonauts (genus Argonauta, the only extant genus in the Argonautidae family) are a group of pelagic octopuses. They are also called paper nautiluses, referring to the paper-thin eggcase that females secrete. This structure lacks the gas-filled chambers present in chambered nautilus shells and is not a true cephalopod shell, but rather an evolutionary innovation unique to the genus Argonauta. It is used as a brood chamber and for trapped surface air to maintain buoyancy.

Argonauts are found in tropical and subtropical waters worldwide; they live in the open ocean, i.e. they are pelagic. Like most octopuses, they have a rounded body, eight arms and no fins. However, unlike most octopuses, argonauts live close to the sea surface rather than on the seabed. Argonauta species are characterised by very large eyes and small distal webs. The funnel–mantle locking apparatus is a major diagnostic feature of this taxon. It consists of knob-like cartilages in the mantle and corresponding depressions in the funnel. Unlike the closely allied genera Ocythoe and Tremoctopus, Argonauta species lack water pores.

Of its names, "argonaut" means "sailor on the Argo"; "nautilus" is derived from the Greek ναυτίλος, meaning "sailor", because it was formerly supposed that Argonauta used their shell-secreting arms as sails when they were at the surface.

The chambered nautilus was later named after the argonaut, but belongs to a different order, the Nautilida.