Argonauts

Phil

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OK, it seems a pity that these obscure little octopods are so rarely mentioned on these pages.

What's going on with these animals? Here we are with this advanced octopus that insists on creating a very ancient ammonite-like shell in which to breed its young. How is this? Is this coincidence or not?

How well studied are these animals? Has anyone ever kept them in captivity?
 

Architeuthoceras

Architeuthis
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Aint those the guys what sailed with Jason, after the golden fleece?

Dr. Woods posted this site on the Ceph list.
Argonauts

If the argonaut has the ability to secrete a shell with its arms, why would it need to copy an ammonoid shell. If the argonaut was using empty ammonoid shells for a nest in the mesozoic how did it remember what an empty ammonoid shell looked like by the time they developed the ability to secrete one that looked like an ammonoid shell? Seems to me it would be easier to just use some other shell for a nest, than to spend years trying to figure out how to secrete one. :bonk: This would foul-up my theory that the octopods learned to coil their arms to look like a school of ammonoids (pedators would grab an arm, thinking it was an occupied shell).

There is probably a little "coiled shell" in all of us. :biggrin2:

They are fabulous animals.
 

Phil

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Another problem with linking ammonoids to argonauts is the length of time elapsed between the extinction of the ammonites, i.e 65 mya, and the earliest recorded argonaut, i.e 25mya. How could an octopod retain some form of ancestral memory for 40 million years before deciding it suddenly wanted to secrete ammonoid-type shells? (Argonaut date here taken from the Tree of Life pages). Even given that the fossil record is incomplete, this seems an unlikely amout of time to have passed with no fossil argonaut shell remains if they were out there in the immediate post-Cretaceous. :grad:

In addition, the chambered ammonite shell was composed of aragonite, the unchambered argonaut calcite. The more one thinks about the theory the more ridiculous it sounds! It's all coincidence in appearance, I'm sure.

:ammonite: :arrow: :bluering: = x
 

cthulhu77

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The more you see and learn, the more things just don't seem to make much sense...I am sure there is an underlying rythym to all of it, but I , for one, seem to be left out of the dance!
Fascinating subject Phil...it never occured to me at all...most perplexing.
greg :oops:
 
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Hi,

I collect cephalopod shells and specialise in animals of the genus Argonauta and Nautilus (though I couldn't even spell the screen-name I wanted right :oops: :bonk: ). Does anyone how many species there are?
I'm sure that more than one species is being treated under the name Argonauta hians due to the diversity in shell shape, size and colour.

Michael.
 

Steve O'Shea

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Hi Michael.

It found is extremely difficult to describe the animals of any of these Argonauta species because they were almost always removed from the shells (with collectors having separated them). The literature is also full of inconsistent and partial descriptions of anatomical characters/character states, and usually for the female only (the male of any species is actually quite poorly described).

It would make for a superb Masters thesis!!! Secure animals with shells and then describe the morphology and anatomy of each. As the hectocotylus of the male is detached and ?swims to the female's mantle, becoming lodged around the base of her gills, detailed examination of these detached structures (often up to 6 per female, mutiple paternity) might enable someone to identify the male morphology of each species (especially if a male with attached hectocotylus is found).

As for A. hians and how many species are being confused with it, it would be very nice to see some of the variation you are encountering in this species. Any chance of a series of photos online?
Kindest
Steve
 
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Argonauta photos

I've hosted all the photos described below here: http://www.picturetrail.com/gallery/view?p=999&gid=4081363&uid=2101892&members=1 (Note: The pictures are of a high resolution so they may take some time to load.)

The first photo is of Argonauta hians "No. 1" which seems to be a very common type. Shells of this Argonaut are usually cream or light sepia in colour and are quite compact. The shell's surface is very smooth with ribs which are barely visible. The tubercles (knobs on top of the shell) are very small and rounded. I have found that shells of this type of A. hians usually don't get very large. Most specimens which I have seen are below 6 cm in size and I have never seen any over 9 cm. Most representatives of this form seem to come from the Philippines.

The second and third photos is of Argonauta hians "No. 2" which seems to be uncommon. This type seems to grow much larger; i have seen numerous specimens past 10 cm (I myself have a shell of 122 mm, a WRS). The shells of this variant of hians usually have a much darker colour (dark brown to even black) and display much more prominent tubercles and ribbing. They also display large "spikes" protruding from both sides of the shell (visible in the second photo of the representative of this variant). A. hians "No.2" seems to be most abundant in the waters surrounding Taiwan and Japan.

Photos 4 through to 6 display different specimens of Argonauta boettgeri, a species often confused with A. hians. These shells seem to be the smallest of all the paper nautiluses (the WRS is listed at a mere 61.9 mm). A. boettgeri originates from Southern Africa (especially Mozambique, where most specimens are from). These are rare finds and vary wildly in degree of pigmentation (as can be seen in the three pics), but most seem to be of a dark colour (dark brown/black). The specimen from S. Africa in photo No. 6 seems to be an "albino", displaying almost a complete lack of pigmentation (sorry for the bad photo - it's the best one I could take o_0). Another characteristic of this species is that the shells are usually finely granulated and display promiment tubercles and well developed ribs (which are usually "wavy"), which alternate in length (one long, one short, etc.).

Photo number 7 is of the very rare Argonauta nouryi. The shell pictured is 87.3 mm in length (my other specimen is 93.9 mm - WRS?), which is at the higher end of their size range. This is one of the rarest Argonauta species and can only be found in the waters around Mexico and Baja California. If my memory serves me well then there have only been two known strandings of this species (both my shells came from the 1992 stranding). The shells of this species cannot be confused with any other being probably the most elongate of any paper nautilus. The shells are of a white or cream colour (with the oldest tubercles having a brownish pigmentation) and possess numerous small knobs on the keel. The surface of the shell is very smuth and has a large number of underdeveloped ribs.

The final photo is of a curious specimen of a shell which seems to share traits of several different species. For the most part it looks like A. boettgeri: it is of a dark colouration and displays very prominent tubercles and ribbing (having the characteristic "wavy" shape). It is also finely covered in small "granules", another characteristic feature of A. boettgeri shells, but it is well outside its normal size range at 75 mm (which would make it the World Record Size by almost 1.5 cm) and displays those prominent spikes which in the description for A. hians "No. 2". Also, this specimen came from Taiwan waters, on the other side of the world when compared to the known distribution of A. boettgeri. Could it be A. cornuta?? I am not sure as the few photos which I have seen that supposedly show this species are very conflicting and also do not seem to show a distinct species. Due to the lack of knowledge on this subject I cannot positively identify it for the moment.

Please let me know if you would like to see any more Argonauta (or Nautilus) shells as my collection consists of over 80 specimens, so this is only a small fraction of it.
Also, I would be interested to know if anyone knows how large Nautilus shells actually get or has any information on the validity of the species Nautilus repertus. In the 2001 edition (newest) of "The Registry of World Record Size Shells" the largest Nautilus pompilius specimen is listed at 253 mm. A shell which I received labelled Nautilus repertus is considerably larger than this at 268 mm, so I am curious as to how large these creatures actually get.

Look forward to reading your replies,
Michael.
 
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