 The sensory organs of bivalves are not well developed and are largely located on the posterior mantle margins . The organs are usually mechanoreceptors or chemoreceptors , in some cases located on short tentacles . The chemoreceptor cells taste the water and are sensitive to touch . They are typically found near the siphons , but in some species , they fringe the entire mantle cavity . The osphradium is a patch of sensory cells located below the posterior adductor muscle that may serve to taste the water or measure its turbidity , but is probably not homologous with the structure of the same name found in snails and slugs . <unk> within the organism help the bivalve to sense and correct its orientation . Each statocyst consists of a small sac lined with sensory cilia that detect the movement of a mineral mass , a statolith , under gravity . In the order Anomalodesmata , the inhalant siphon is surrounded by vibration @-@ sensitive tentacles for detecting prey . 
