Malleolus (arthropod)

Malleolus (plural: malleoli) is a fan-shaped chemoreceptor or Racquet Organ, an array of which are carried in pairs on the ventral or undersides of Solpugidae. They are the counterpart of pectines in scorpions, and modified walking limbs in the uropygids and amblypygids. Most species have 5 pairs of malleoli on the ventral surface of the fourth pair of legs of both sexes, while juveniles and other species have 2-3 pairs.
A malleolus comprises a basal stalk and a triangular fan, with epicuticular protrusions on each anterior face, and granular structures on each stalk, with undulate surfaces at each distal end.