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 ) 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