Every Conus I have cut or broken open retains all of the internal
structure, but the walls are partly resorbed... until they are
paper-thin and transparent. These walls can be weak enough that when
shaking a partly water-filled shell to try to shake out bits of
animal, the walls can break and fall out.

I'm sure Geerat Vermeij would say that this is metabolic economy,
whereby tit costs the animal less to resorb and reuse its own
shell-material than to extract it from seawater. It also has the
bybenefit of significantly lightening the shell without significantly
structurally weakening it.

Other taxa which resorb inner whorls (in these cases resorbtion is complete):
Neritidae
Olivellidae
Cysticidae
Ellobiidae
--
Regards
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
Mollusc, Toyota & VW van fan

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