Practice question

Molluscan body plan consists of three main regions: muscular ventral foot used for creeping locomotion, burrowing and attachment, dorsal visceral mass containing digestive gland, heart, gonads and kidney, and mantle or pallium enveloping visceral mass dorsally, secreting shell and delimiting mantle cavity housing ctenidia for respiration and chemoreception. Shell is mantle product, not independent body region, radula is feeding organ within buccal mass. Visceral mass often undergoes torsion in gastropods. This foot-mantle-visceral mass triad represents conserved synapomorphy uniting all molluscan classes Polyplacophora, Gastropoda, Bivalvia, Cephalopoda, Monoplacophora and Scaphopoda morphologically.