mollusca

• from Latin, “mollis” which means “soft.
• Free-living or occasionally parasitic
• bilaterally symmetrical, unsegmented, often with definite head
• Triploblastic body
• Coelom limited mainly to area around heart, and perhaps lumen of gonads, part of kidneys, and occasionally part of the intestine
• Body plan has a head-foot portion and a visceral mass portion.
• Dorsal body wall forms pair of folds called the mantle, which encloses the mantle cavity, is modified into gills or lungs, and secretes the shell
• absent in some); Ventral body wall specialized as a muscular foot, variously modified but used chiefly for locomotion; radula in mouth
• Complex digestive system; rasping organ (radula) usually present; anus usually emptying into mantle cavity; internal and external ciliary tracts often of great functional importance
• Nervous system of paired cerebral, pleural, pedal, and visceral ganglia; ganglia centralized in nerve ring in gastropods and cephalopods
• Trochophore larvae, spiral cleavage, and schizocoelous coelom formation
• No asexual reproduction; Both monoecious and dioecious forms
• Class Gastropoda - Shell, when present, usually coiled; body symmetry distorted by torsion; some monoecious species.

  
• Class Cephalopoda - Foot modified into a circle of tentacles and a siphon; shell reduced or absent; head in line with the elongate visceral mass

  octopus
• Class Bivalvia - Body enclosed in a shell consisting of two valves, hinged dorsally; no head or radula; wedge-shaped foot.

  Giant Clam
• Class Scaphopoda - Body enclosed in a tubular shell that is open at both ends: tentacles used for deposit feeding; no head.