(in a coelenterate) a filament at the mouth of a nematocyst which triggers the emission of the stinging hair when touched.
- ‘At the narrow outer edge of the cnidocyte is a short trigger hair.’
- ‘When the trigger hair on the outside of a nematocyte is touched, a coiled thread tube inside the enclosed nematocyst is released.’
A bristle on the leaf of a Venus flytrap which triggers the closure of the leaf around an insect.
- ‘The flytrap features a set of inch-long, heart-shaped capture leaves, each fringed with trigger hairs and bisected by a deep fold.’
- ‘Darwin's investigation into the biology of the Venus flytrap involved testing the sensitivity of trigger hairs.’
- ‘The trap does not close every time a trigger hair is touched because a lot of energy would be used up this way.’
- ‘The first phase of the leaf closure begins when a trigger hair is disturbed.’