A sensillum (plural sensilla) is an arthropod sensory organ protruding from the cuticle of exoskeleton, or sometimes lying within or beneath it. Sensilla appear as small hairs or pegs over an individual's body. Inside each sensillum there are two to three sensory neurons. These neurons, or receptors, gather information about environment the arthropod is in: * Chemoreceptors (i.e. trichoid, basionic, coeloconic, placodea) * Mechanoreceptors (e.g.: campaniform sensilla) * Thermoreceptors * Hygroreceptors