Knobby argonaut

Taxobox
name = Knobby argonaut

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image_caption = Eggcase of "Argonauta nodosa"
regnum = Animalia
phylum = Mollusca
classis = Cephalopoda
ordo = Octopoda
familia = Argonautidae
genus = "Argonauta"
species = "A. nodosa"
binomial = "Argonauta nodosa"
binomial_authority = Lightfoot, 1786
synonyms =
*?"Argonauta oryzata"
Meuschen, 1787
*"Argonauta tuberculata"
Roding, 1798
*"Argonauta tuberculosa"
Lamarck, 1822 "in" 1815-1822
*"Argonauta gracilis"
Kirk, 1885

The knobby or knobbed argonaut, "Argonauta nodosa", 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. [cite book | author = Pisor, D. L. | year = 2005 | title = Registry of World Record Size Shells | edition = 4th edition | publisher = Snail's Pace Productions and ConchBooks | pages = p. 12] "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.cite book | author = Norman, M. | year = 2000 | title = Cephalopods: A World Guide | publisher = ConchBooks | pages = p. 192] 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. [cite web | author = Lu, C. C. | work = Australian Biological Resources Study | url = http://www.deh.gov.au/cgi-bin/abrs/fauna/details.pl?pstrVol=CEPHALOPODA;pstrTaxa=89;pstrChecklistMode=2 | title = Argonautidae | accessdate = 2006-09-13]

"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. [fr icon cite journal | author = Rancurel, P. | year = 1970 | title = Les contenus stomacaux d' "Alepisaurus ferox" dans le sud-ouest Pacifique (Céphalopodes) | journal = "Cah. O.R.S.T.O.M. Ser. Océanogr. | volume = 8 | issue = 4 | pages = 4–87] "A. nodosa" has also been found in the stomach contents of Australian Fur Seals, "Arctocephalus pusillus doriferus", in the Bass Strait and southern Tasmania. [cite journal | author = Gales, R., D. Pemberton, C. C. Lu & M. Clarke | year = 1994 | title = The cephalopod diet of the Australian fur seal: variation due to location, season and sample type | journal = Aust. J. Mar. Freshwater Res. | volume = 44 | pages = 657–671 | doi = 10.1071/MF9930657]

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. [cite journal | author = Reid, A. | year = 1989 | title = Argonauts: ancient mariners in boats of shell | journal = Aust. Nat. Hist. | volume = 22 | issue = 12 | pages = 580–587] Similar development has been observed in the egg masses of "Argonauta bottgeri". [cite journal | author = Nesis, K. N. | year = 1977 | title = The biology of paper nautiluses, "Argonauta boettgeri" and "A. hians" (Cephalopoda, Octopoda), in the western Pacific and the seas of the East Indian Archipelago | journal = Zool. Zh. | volume = 56 | pages = 1004–1014]

"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.

The type specimen of "A. nodosa" was collected off the Cape of Good Hope. The type repository is unknown. [ [http://www.mnh.si.edu/cephs/newclass.pdf Current Classification of Recent Cephalopoda] ]

References

* Sweeney, M. J. (2002). [http://www.tolweb.org/accessory/Argonautidae_Taxa?acc_id=2464 Taxa Associated with the Family Argonautidae Tryon, 1879.] "Tree of Life web project".

External links

* [http://tolweb.org/tree?group=Argonauta Tree of Life web project: "Argonauta"]