Squid Beaks and Surgical Implants

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?
 
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."
 
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.
 
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...
 

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