A 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 as well as the pedipalps in spiders and other arachnids.[1][2] Generally, solifuges have 5 pairs of malleoli on the ventral surface of the fourth pair of legs. malleoli are usually larger in males.[3] 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.