Purty Molluscs

um...

Architeuthis
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I just realized that yesterday was my one-month tonmoversary. I'm going to use this as an excuse to have a little extra :beer:, and I invite everyone to do the same (provided you have achieved the relevant legal drinking age).

You know you want to.


(and remember: JD and Coke might be a good mix, but drinking and driving aren't!)
 

um...

Architeuthis
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Steve O'Shea said:
um... said:
I just realized that yesterday was my one-month tonmoversary.
Happy Tonmoversary um...... It's been great to have you online
Cheers
O
Thank-you, sir. It's certainly great to be here, interacting with like-minded individuals for a change.

tonmo.com is my happy place.
 

Melissa

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Thanks! Now I know what I'm reading tonight, when I should be writing :(

Melissa
 

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Messenger (2001) seems inclined to think that "the chromatophores may have evolved primarily for concealment" from "sharp-toothed predators", which became necessary as the external shell was lost. How effective was the shell at keeping predators from eating the occupants? In Ammonites ( :thumbsup: :thumbsup: ), Monks and Palmer write:

Ultimately, cephalopods have had to trade-off increased mobility and swimming efficiency against the defensive properties of the shell. The shell can be thought of as being under a constant 'crushing attack' from the surrounding water. The thinness of the shell and the lack of structural support between each septum, mean the shell has little extra strength to resist the additional forces from a predator's bite.
The shell is obviously going to provide some measure of protection, but more sturdiness will eventually come at the expense of buoyancy. Looking at an ammonite shell, I get the impression that buoyancy is a pretty big deal.

Andrew Gray, in Shell loss in mollusc evolution, suggests that:

The internalisation of the shell provides coleoids with several advantages, most of which are related to the development of more efficient swimming. (The coleoids may originally have evolved in response to increasing competition from predatory fish, with which they are convergent in many ways.) Liberation from an external shell helps the coleoids to float horizontally in the water, and has allowed the development of fins for better locomotion, and a highly contractible mantle cavity that can squirt out water violently, moving the animal by jet propulsion.
Basically, I'm getting back to my Jean-inspired epiphany of several posts ago: Might the early development of body patterning have been driven by its use in communication at least as much as by its use in concealment?

If the shell is overrated as a defensive adaptation, and coleoids end up being more mobile (and presumably harder to catch) without large external shells, how badly would crypsis be needed? I'm also making the big assumption here that a chromatophore system in the very early stages of development would not be anywhere near as effective as the finished product, and might even be occasionally harmful.

Anyone care to set me straight?

:bonk:
 

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Architeuthis
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Hmm…

OK, here’s a bit of a half-baked argument against what I just said.

Consider the case of a young early coleoid, possibly living a life something like a young cuttlefish’s (i.e., benthic). This guy is bite-sized and can’t do as much running or fighting as his larger conspecifics. He is in much greater need of camouflage, since hiding is going to be his shtick. Perhaps early chromatophore systems produced less structured patterns that were more along the lines of Disruptive, and were in fact sufficient to provide some degree of protection for this little guy when hiding over a mottled rocky bottom or partially burying himself into sand. Breaking up his outline might be a good start, even if he can't blend into the background as well as a modern octopus could.

That still leaves me with a million questions…

:confused: , and still :bonk:
 

Melissa

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um...

You aren't talking to yourself, we're just still thinking it through and reading to catch up enough to offer a reply. I should have one around November 14 at the earliest!

Melissa
 

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