Body asymmetrical, depicts torsion or its effects; shell coiled in most, well developed head with radula, large flat foot, gills one or two or with pulmonary cavity (lung); mainly with single auricle and single kidney. Nervous system with cerebral, pedal, pleural and visceral ganglia usually with trochophore and veliger larvae. Gastropods, the biggest class of molluscs, show extensive adaptive radiation, comprising adapted to life for bottom as well as pelagic and littoral existence in sea. They have as well invaded fresh water and many have successfully conquered land also. In this subsection you will study the organisation of their body.