|Eggcase of Argonauta nodosa|
Argonauta nodosa, 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. A. nodosa produces a very characteristic shell, which is covered in many small nodules on the ridges across the shell, hence the specific epithet nodosa and common name. These nodules are less obvious or even absent in juvenile females, especially those under 5 cm in length. All other argonaut species have smooth ridges across the shell walls.
A. nodosa 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. It is only known from the Southern Hemisphere.
A. nodosa is thought to feed primarily on pelagic molluscs. Captive females have been observed readily taking dead prawns and fish. The species is preyed on by numerous predators. It has been reported in the stomach contents of Alepisaurus ferox from the south-western Pacific. A. nodosa has also been found in the stomach contents of Australian fur seals, Arctocephalus pusillus doriferus, in the Bass Strait and southern Tasmania.
Females grow to 100 mm ML and 300 mm total length, while males do not exceed 40 mm in length. 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".
It has been reported that the egg clusters of A. nodosa from southern Australia can be clearly divided into three portions, each with eggs at a similar developmental stage. Similar development has been observed in the egg masses of Argonauta bottgeri.
A. nodosa 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.
One of the earliest known depictions of A. nodosa, from Index Testarum Conchyliorum (1742) by Niccolò Gualtieri
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- Current Classification of Recent Cephalopoda