Squid Beaks and Surgical Implants | The Octopus News Magazine Online
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Squid Beaks and Surgical Implants

Fujisawas Sake

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#3
I'm sure I've asked this before, but of what material are cephalopod beaks composed? I'm guessing keratin, or something similar, but is any metal used? (Thinking of the radulla of certain marine snails here)
 

Fujisawas Sake

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#8
Actually calcium has some issues as to fixing under high pressure, so chitin or a protein works better
 

monty

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#9
so, obviously cuttlebones (presumably including spirula) and nautilus shells are calcium based... are squid pens and the vestigial shells of some octos also rather than chitin? How about statoliths? I know squid sucker rings are also chitinous. How about radulas? and yeah, I could probably look this stuff up if I wasn't lazy... Is it pretty much across-the-board that all cephs can make both calcium and chitin based hard bits?
 

monty

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#12
Jean;119574 said:
gladii (pens) are chitinous also, as is the radula. Statoliths are calcareous.


J
So I guess that implies that somehow the system that builds the gladius, which seems pretty likely to be homologous to the cuttlebone and shell, somehow changed, within the decabranchia, to be chitinous (and non-chambered) somehow... I wonder if that involved a regulatory switch in the gene battery used to make it all at once, or if there was a chitinous component to the calcite that remained when the calcite was lost, or what. And now I really want to know what the vestigial shells in octopus are made of, since they clearly diverged earlier than squids and cuttles (and I need to check if vampyroteuthis has some homologous internal structure.) I'll mention the (probably) red herring to avoid that the argonaut shell is not believed to be homologous to the structures we're talking about, although that then raises a lot of questions about why its shape is so similar to ammonite shells.

off to tolweb and google...
I'm back, did you miss me?

results: vampyroteuthis has a chitinous gladius, spirula is calcareous as expected, cirrata have a shell with "cartilage-like structure" and incirrata have "stylets" including Haliphron atlanticus with a "gelatinous" shell (not clear what it's made of) and some other octopodidae have "stylets" which are described both as cartilaginous and "often mineralized."
 

monty

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#14
Keith;119581 said:
wow. i am now way out of my league. i just had to google like every other word in that statement.
I hope I didn't misspell too many of them...

Actually, I didn't use the word that probably sums up a lot of my thinking: polyphyly, or, more specifically, my curiosity that chitonous shell/gladius/pen/cuttlebone/stylet material might be polyphyletic, in that it occurs in both the decabranchians like squids, but also the octopods like octopus and vampyroteuthis, which would mean that the last common ancestor had a calcium-based shell material which was lost somehow in both squids and octopuses, but not in some of their shared ancestors. When this happens, it's interesting because it either means that the ancestor had a predisposition to this trait, so it was easy to happen in two separate lineages, or that there is an immense selection pressure for it (which seems unlikely here). I suspect that belemnites had both a calcareous phragmacone shell part, and a chitinous pen analog, and that could be the commonality, since vampyroteuthis having a chitin squid-like pen pretty much proves that it's there fully formed in both lineages, unless there's a major mistake in the accepted phylogeny (evolutionary tree) of coleoid cephs... that possibility is what makes polyphyletic traits very interesting to biologists, in the sense that science makes the most progress not in "just as a thought" moments but rather "that's funny, I didn't see that coming" observations.
 

cuttlegirl

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#15
monty;119579 said:
So I guess that implies that somehow the system that builds the gladius, which seems pretty likely to be homologous to the cuttlebone and shell, somehow changed, within the decabranchia, to be chitinous (and non-chambered) somehow...
Hmm... The gladius has ridges in it, which might be growth lines. I need to do some more reading before replying on analogies to cuttlebones...
 

Jean

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#16
cuttlegirl;119592 said:
Hmm... The gladius has ridges in it, which might be growth lines. I need to do some more reading before replying on analogies to cuttlebones...
weeelllllll they're not as defined as an actual ridge (at least not in N. sloanii :roll:) See attached piccy in the word doc!

not sure how they originate however I know that the increments in bivalve shells are calcium (and/ or aragonite) in a protein matrix, so perhaps the calcium has been lost and the protein matrix remains.

J
 

monty

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#18
How's this, then:

Squids have a pen made of chitin, like crab shells. Cuttlefish have, in the same place, a cuttlebone made of some calcium stuff like a seashell... but some octopuses and their relatives have something like the pen also made of chitin. This is weird, because squids and cuttles are supposed to be more closely related to each other than they are to octopuses, but it's pretty much believed that their last common ancestor had a calcified internal shell like the cuttlefish. Did the squids and octopuses lose their shells in the same way? What would this tell us about how they're related or what the last common ancestor was like, since squid- and octopus-like animals haven't left much of a fossil record?

I'm not trying to be too jargon-heavy, it's just sometimes easier to express things the way they're discussed in papers, and anyway, I need some practice with some of this stuff. On the other hand, if you can't explain something without jargon, it's usually a sign that you don't understand it, so writing the version in this post is probably character-building for me as well.
 

monty

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#20
Keith;119634 said:
oh no that wasnt sarcasm. my bad
oops, my bad, too, I guess... but it did get me to wake up and think about how much I was using two dollar words where it wasn't really that important to my point. It's an interesting exercise to put the "use the vocabulary in a context where people can learn it" version next to the "how can this be explained so that it makes sense directly" version.

Like I said in another recent post, one of the things I like about TONMO is that there's a range from professional researchers to grade school students, so it's worthwhile trying to make sure we cover all the bases... of course, we'll probably always have both academic discussions and enthusiastic novice questions, and shouldn't have every discussion cover both, but this got me thinking about looking for opportunities to cover a wider range...
 

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