·noun ·pl A division of Arachnoidea, including the daddy longlegs or harvestman (Phalangium) and many similar kinds. They have long, slender, many-jointed legs; usually a rounded, segmented abdomen; and chelate jaws. They breathe by tracheae. Called also Phalangides, Phalangidea, Phalangiida, and Opilionea.