Although the actual function of trichocysts is still unclear, scientists believe that these projectile organs are mainly used as defensive mechanisms in response to mechanical or chemical stimuli. Trichocysts are commonly found in ciliated organisms, such as paramecia and other types of protists.
Extrusive cellular structures called extrusomes have the ability to eject their contents, often in an explosive manner, when exposed to an external stimulus. In addition to trichocysts, some extrusomes that are present in ciliated organisms include mucuocysts, haptocysts and toxocysts.
Trichocysts are thin, pointed structures containing proteins that are poisonous in some species. When used for self-defense, the toxin in the discharged threads paralyzes nearby threatening organisms. Non-toxic trichocysts, such as those in paramecium, are said to anchor the microorganism to solid surfaces. In other ciliated protists, trichocysts are used to capture prey.