bio

Lateral line

A row of sensors running down each flank of a fish and some amphibians, reading the flow and pressure of the surrounding water. Inside are sensory units called neuromasts - clusters of hair cells wrapped in a jelly cap; as water pushes past, the jelly tilts, bending the hair cells and firing a nerve impulse. This lets a fish feel the velocity, direction, and swirl of a nearby swimmer it cannot see - which is how a whole school can turn at once as a single body. It is a purely aquatic sense, because it reads the motion of a fluid.