Many acariform mites (especially Oribatida) have a pair of well developed bothridial sensilla (see Character 26d) on the prodorsum. The cup-like bases (bothridia) of these structures resemble a stigmatal opening and were once thought to be respiratory organs, but apparently this is rarely true, and their primary function appears to be sensing air currents. The sensilla come in various shapes, from setiform to pectinate to plumose to club-shaped. They are variously called pseudostigmatic organs, trichobothria, or bothridial sensilla.
Two pairs of often long and plumose trichobothria can be found on the prodorsa of some prostigmatans, and rarely the second pair is found on the rear end of the hysterosoma.
Only mites have trichobothria on the prodorsum. In other arthropods the sensilla are on the legs, pedipalps, rarely on the head (e.g., polyxenid millipedes), or arranged serially on the trunk.
Mites sometimes have trichobothria on the legs (usually tibiae I and/or IV), and more often have 1–2 pairs on the body (usually the prodorsum). In some myriapods (pauropods, symphylans) the trichobothria are present as segmental pairs (usually only one pair in symphylans).
Author: David E. Walter
Content last updated Sept. 2006, unless indicated otherwise
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