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."