ABSTRACT
Molluscs, meaning “soft animals”, is a misnomer: For most, the key feature is a hard, mostly mineralized external shell growing by accretion. More properly, one should talk of the shell/mantle structure because it is the feedback between the soft skin duplicature (“mantle”) and its rigid counterpart (“shell”) that allows this complex to grow beyond the contour of a soft hydrostatic body. This shell provides support, protection and a water-flushed mantle cavity that allows respiration through both the mantle and soft, featherlike body appendages (gills) hanging freely in the cavity. Another basic molluscan feature is a foot, whose broad sole moves the body over the substrate either by cilia or waves of muscular action. The most primitive mollusc would have been a limpet-like animal living on rocks or biomats.
