4. (Arthropoda: Insecta) a. In Lepidoptera, the frenulum; wing coupling device. b. In Collembola, hamula that holds the furcula in place in springtails. c. In Hymenoptera, the ring that prevents the sting from being darted out too far. d. In Coleoptera larvae, a fixed sclerotized, tooth-like structure on the mandible.