A sensillum (plural ''sensilla'') is an

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, o ...

sensory organ A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system rec ...

protruding from the

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

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 four sensory neurons. These neurons, or receptors, gather information about environment the arthropod is in: * Chemoreceptors (i.e. trichoid, basionic, coeloconic, placodea) *

Mechanoreceptors A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...

(e.g.:

bristle sensilla Bristle sensilla (sometimes also called tactile hairs) are a class of mechanoreceptors found in insects and other arthropods that respond to mechanical stimuli generated by the external world. As a result, they are considered exteroceptors. Brist ...

campaniform sensilla Campaniform sensilla are a class of mechanoreceptors found in insects, which respond to local stress and strain within the animal's cuticle. Campaniform sensilla function as proprioceptors that detect mechanical load as resistance to muscle contr ...

, hair plates, chordotonal neurons) * Thermoreceptors * Hygroreceptors Most sensilla are specially shaped according to the type of information they are gathering. In spiders,

slit sensilla The slit sensilla, also known as the slit sense organ, is a small mechanoreceptory organ or group of organs in the exoskeleton of arachnids which detects physical deformation or strain due to forces experienced by the animal. The organ appears in ...

are used to detect substrate vibrations, while trichobothria are used to detect air-borne vibrations.

Chemoreceptors

Chemo-reception is one of the most dominant senses in the insect kingdom. Many arthropods use chemical signals to locate food, shelter and mates. Other invertebrates have similar sensory organs also referred to as sensilla; these consist of various papillae or ciliated areas of the cuticle connected to sensory neurons and occur in

velvet worms Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus ...

tardigrades Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär ...

and leeches.

References

Arthropod anatomy {{insect-anatomy-stub