Cuticular hair organs evoking reflexive closing and opening of the crayfish claw

Abstract

1. 1. Cuticular hair organs on the index of the propus of the chelae of the crayfish Procambarus simulons simulons Faxon evoke reflexive closing and opening of the dactyl when stimulated by touch. 2. 2. These receptor organs are arranged in eight linear fields (A-H), with each row innervated by a separate branch of an afferent nerve. 3. 3. Nerve branches A and F innervate receptors on either side of the cutting edge of the propus; these organs trigger claw closing. Branches B and G innervate receptors driving both claw opening and closing; branchs C, D, E and H innervate hair organs that drive claw opening. 4. 4. The hair organs, which consist of groups of simple or pappose setae, can be divided into four types based on morphology. 5. 5. The cuticular hair organs show directional sensitivity.