The slit sensilla, also known as the slit sense organ, is a small

mechanoreceptory 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, a ...

organ or group of organs in the

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton ( endoskeleton) in for example, a human. In usage, some of the ...

arachnid Arachnida () is a class of joint-legged invertebrate animals ( arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and ...

s which detects physical deformation or strain due to forces experienced by the animal. The organ appears in the vast majority of discovered arachnids, and is "remarkably consistent" in location and direction within each

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

. The arachnid slit sensilla corresponds to the

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 cont ...

found in insects. Slit sensilla tend to be widely distributed over the arachnid's exoskeleton, but have also been found to be grouped at specific locations and in a bundle of parallel lines; the latter distribution is referred to as a "lyriform organ". The term "lyriform organ" comes from the shape of such grouped slit sensilla, which resembles a

lyre The lyre () is a stringed musical instrument that is classified by Hornbostel–Sachs as a member of the lute-family of instruments. In organology, a lyre is considered a yoke lute, since it is a lute in which the strings are attached to a ...

. Arachnids with lyriform slit sensilla are commonly used as experimental subjects for investigations into

mechanosensation Mechanosensation is the transduction of mechanical stimuli into neural signals. Mechanosensation provides the basis for the senses of light touch, hearing, proprioception, and pain. Mechanoreceptors found in the skin, called cutaneous mechanorecept ...

because the almost 2D structure of their slit sensilla allows for relatively simple understanding of the system; thus, the results of

electrostimulation Electro-stimulation is stimulation using electricity. It can be used in the context of: * Animal husbandry as part of the artificial insemination process * Bioelectromagnetics ** Cranial electrotherapy stimulation ** Transcranial magnetic stimul ...

on such arachnids can be easily recorded. Etymologically, "slit sensilla" are so named because they resemble a channel penetrating through the exoskeleton into the animal; despite this appearance, however, investigation has shown that slit sesilla do not actually penetrate the

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

of the exoskeleton, but merely represent a thinning of the material.

References

Bibliography

* *{{cite journal, last1=French, first1=Andrew S. , last2=Torkkeli , first2=Päivi H. , last3=Seyfarth , first3=Ernst-August , date=2002, title=From stress and strain to spikes: mechanotransduction in spider slit sensilla, journal=Journal of Comparative Physiology A, publisher=Springer-Verlag, volume=188, issue=10, issn=0340-7594, doi=10.1007/s00359-002-0363-1, pages=739–752, pmid=12466950, s2cid=308783 Spider anatomy Sensory receptors