Trichobothria

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Trichobothria (singular trichobothrium) are elongate setae, present in the arachnids, that function in the detection of airborne vibrations and currents.

[edit] Morphology

Unlike the ordinary setae, which are tapered, the trichobothria have the same gauge on all their extent. They fit into the bottom of a broad and deep cup to which connects a membrane with extreme flexibility which adds an extraordinary mobility to them. The least air vibration is able to put them moving and to excite the small group of sensory cells which ensures their innervation. See figures below for details (from Foelix, 1996):

Mechanosensitive hair sensilla from a leg of the wolf spider Lycosa gulosa. The slender trichobothrium(Tr) arises vertically from a prominent socket; the stronger tactile hair (T) emerges obliquely from a less-developed socket. 1,250x.

Innervation of a trichobothrium of the house spider Tegenaria, longitudinal section.

[edit] Distribution

Trichobothria are present in most orders of the Arachnida, except in Solifugae, Ricinulei and Opiliones (Grassé, 1949). Although the distribution of trichobothria on the bodies of arachnids is often used by systematists (especially in Scorpiones and Pseudoscorpiones), few interordinal patterns are apparent (Shultz, 1990).

[edit] References

• Foelix, R.F., 1982. Biology of Spiders. Harvard University Press. Cambridge, Massachusetts, and London, England.
• Grassé, P. (1949). Traité de Zoologie: Anatomie, Systématique, Biologie / publié sous la dir. de M. Pierre-P. Grassé. tome VI, Onychophores - Tardigrades - Arthropodes - Trilobitomorphes - Chélicérates. - Masson et Cie, Paris.
• Shultz, J.W. (1990). Evolutionary Morphology And Phylogeny of Arachnida. Cladistics 6: 1-38.