geronimo - Thanks! I had hoped you'd jump in with an answer.
Badger Loving Fluffster (Ben, I assume) - That's exactly the kind of response I expect from frothers (although in all honesty, perhaps a little more heavy on swearwords)! The five plates was sheer luck (i.e. an esthetic decision), as you probably guessed. You're absolutely right on the underbelly texture. I started with the image of rolls of fat in mind, but must admit I wandered off a bit while sculpting. The segmentation is something I was still in doubt about after having made the first model (the one with the mouth wide open); I tried to define the segments slightly more in the next two, in accordance with the carapace sections, but didn't want to stray too far from the first model to keep sufficient coherence throughout. All in all, I think your points are absolutely valid, and a more decisive approach both to the distinction between soft tissue and armour and to the exact nature of the underbelly tissue would certainly have benefited the models. Some more planning in advance would probably have helped; something to keep in mind for further projects.
Duff - Cheers! I'd absolutely love to see what your grubby mitts would do to them.
I really didn't expect this kind of response. What kind of number of casts should I be looking at to make a moulding/casting/selling operation more or less viable?