A sensory system in fish and amphibians consisting of a line of sense organs (neuromasts) running along either flank of the body from head to tail. Each neuromast contains sensory hair cells that are sensitive to vibrations or variations in water pressure and are used to detect moving objects, such as predators or members of the same shoal, and to monitor progress through water during swimming. In amphibians and some fishes, the neuromasts lie on the surface, whereas in most teleost and elasmobranch fishes they are located internally to lateral line canals. These are mucus-filled channels that lie just beneath the skin and connect to the exterior via a series of pores. Only the sensitive cilia of the neuromasts project into the canals.