Argonaut (animal)

Argonauts Temporal range: Miocene – Recent PreꞒ Ꞓ O S D C P T J K Pg N
Female Argonauta argo with its eggs bulging out of its damaged shell
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Order:	Octopoda
Family:	Argonautidae
Genus:	Argonauta Linnaeus, 1758
Type species
Argonauta argo Linnaeus, 1758
Species
Argonauta argo Argonauta boettgeri* Argonauta cornutus* Argonauta hians Argonauta nodosus Argonauta nouryi Argonauta pacificus* †Argonauta absyrtus †Argonauta biarmatus †Argonauta itoigawai †Argonauta joanneus †Argonauta oweri †Argonauta sismondai †Argonauta tokunagai *Species status questionable.
Synonyms
Argonautarius Dumeril, 1806 Todarus nom. nud. Rafinesque, 1815 Todarus Rafinesque, 1840 Trichocephalus Chiaje, 1827 in 1823-1831

The argonauts (genus Argonauta, the only extant genus in the family Argonautidae) are a group of pelagic octopuses. They are also called paper nautili, referring to the paper-thin eggcase that females secrete; however, as octopuses, they are only distant relatives of true nautili. Their 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.^[1] It is used as a brood chamber, and to trap surface air to maintain buoyancy. It was once speculated that argonauts did not manufacture their eggcases but utilized shells abandoned by other organisms, in the manner of hermit crabs. Experiments by pioneering marine biologist Jeanne Villepreux-Power in the early 19th century disproved this hypothesis, as Villepreux-Power successfully reared argonaut young and observed their shells' development.^[2]

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 limbs (arms) and no fins. However, unlike most octopuses, argonauts live close to the surface rather than on the seabed. Argonauta species are characterised by very large eyes and small webs between the arms. 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 of the Argo".^[3] "Paper nautilus" is derived from the Greek ναυτίλος nautílos, which literally means "sailor", as paper nautili were thought to use two of their arms as sails.^[4] This is not the case, as argonauts swim by expelling water through their funnels.^[5] The chambered nautilus was later named after the argonaut, but belongs to a different cephalopod order, Nautilida.