Argonauta nodosus [previously known as ''Argonauta nodosa''<ref>{{Cite journal|last=Finn|first=Julian K.|date=2013|title=Taxonomy and biology of the argonauts (Cephalopoda: Argonautidae) with particular reference to Australian material|journal=Molluscan Research|volume=33|issue=3 |pages=143–222|doi=10.1080/13235818.2013.824854 |s2cid=84533043 }}</ref><ref>{{Cite web|title=Mollusca Base website|url=https://www.molluscabase.org/aphia.php?p=taxdetails&id=1530663|url-status=live|website=Mollusca Base website|archive-url=https://web.archive.org/web/20210823002759/https://www.molluscabase.org/aphia.php?p=taxdetails&id=1530663 |archive-date=2021-08-23 }}</ref><ref>{{Cite web|title=WoRMS website|url=https://www.marinespecies.org/aphia.php?p=taxdetails&id=1530663|url-status=live|website=WoRMS website|archive-url=https://web.archive.org/web/20210823001303/https://www.marinespecies.org/aphia.php?p=taxdetails&id=1530663 |archive-date=2021-08-23 }}</ref>], also known as the knobby or knobbed argonaut, is a species of pelagic octopus. The female of the species, like all argonauts, creates a paper-thin eggcase that coils around the octopus much like the way a nautilus lives in its shell (hence the name paper nautilus). The shell is usually approximately 150 mm in length, although it can exceed 250 mm in exceptional specimens; the world record size is 292.0 mm.[1] A. nodosus produces a very characteristic shell, which is covered in many small nodules on the ridges across the shell, hence the specific epithet nodosus and common name. These nodules are less obvious or even absent in juvenile females, especially those under 5 cm in length.[2] All other argonaut species have smooth ridges across the shell walls.[2]
Females grow to 100 mm ML and 300 mm total length, while males do not exceed 40 mm in length.[2] The specialised webbed arm pair of this species is covered in numerous chromatophores. Mark Norman notes that "the colour of these webs can quickly change from maroon red to reflective silver".[2] It has been reported that the egg clusters of A. nodosus from southern Australia can be clearly divided into three portions, each with eggs at a similar developmental stage.[3] Similar development has been observed in the egg masses of Argonauta bottgeri.[4]
A. nodosus has a relatively wide distribution covering the Indo-Pacific region as well as the eastern coast of South America. The species is most common in southern Australia, New Zealand, and South Africa.[2] It is only known from the Southern Hemisphere.[5] The type specimen of A. nodosus was collected off the Cape of Good Hope. The type repository is unknown.[6] A. nodosus is occasionally involved in mass strandings along the South African and southern Australian coastlines. The strandings are seasonal and generally occur between April and August, towards the end of the animals' spawning season.
A. nodosus is thought to feed primarily on pelagic molluscs. Captive females have been observed readily taking dead prawns and fish.[2] The species is preyed on by numerous predators. It has been reported in the stomach contents of Alepisaurus ferox from the south-western Pacific.[7] A. nodosus has also been found in the stomach contents of Australian fur seals, Arctocephalus pusillus doriferus, in the Bass Strait and southern Tasmania.[8]
In traditional Māori culture of New Zealand, Argonauta nodosa (known as Maori: pūpu tarakihi) is a symbol of new growth and rebirth, as the shape of the animel resembles koru, unfurling fern fronds, which have a similar meaning in art. They are involved in many traditional stories, notably the waiata "He Ata te Hau", which recounts a dream the Ngāti Whātua tohunga Tītahi had of a mass beaching of white Argonauta nodosa driven by the north wind, which became seen as a prophecy of Europeans arriving to New Zealand.[9]