Phylum Mollusca– Dorsal epithelium forming a mantle, which secretescalcareous spicules or shells– Cuticular band of teeth (radula) in the esophagus– Ventral body wall muscles develop into a locomotory orclinging foot– An enormous phylum, including at least 50,000 and asmany as 120, 000 living species– Most molluscs have shells consisting primarily ofcalcium carbonate set in a protein matrix– The shells of most molluscs have a thin, outer organiclayer; a thin, innermost calcareous layer; and a thick,calcareous middle layer