 The sedentary habits of the bivalves have meant that in general the nervous system is less complex than in most other molluscs . The animals have no brain ; the nervous system consists of a nerve network and a series of paired ganglia . In all but the most primitive bivalves , two cerebropleural ganglia are on either side of the oesophagus . The cerebral ganglia control the sensory organs , while the pleural ganglia supply nerves to the mantle cavity . The pedal ganglia , which control the foot , are at its base , and the visceral ganglia , which can be quite large in swimming bivalves , are under the posterior adductor muscle . These ganglia are both connected to the cerebropleural ganglia by nerve fibres . Bivalves with long siphons may also have siphonal ganglia to control them . 
