shell (Scope note)

The term (which in this thesaurus includes CUTTLEFISH BONE) should not be confused with EGGSHELL. Mollusc shell may be composed (wholly or in part) of calcite. But also can be composed (wholly or in part) of aragonite and sometimes both together e.g. mussels, with an outer calcite shell and inner aragonite layer (bimineralic shells).