2. (Arthropoda: Crustacea) a. A well defined projecting ridge on the outer surface of the carapace of podocopan ostracods. b. The unpaired posteriodorsal plate of thoracic barnacles; in lepadomorphs, 1 of up to 4 unpaired plates of the capitulum; in verrucomorphs, the compartmental plate between the rostrum and fixed tergum; in balanomorphs, compartmental plate, with alae on each side, opposite the rostrum.
3. (Arthropoda: Insecta) a. A form of sharp distal cornuti of the genitalia of certain male Lepidoptera. b. For Othroptera see frontal costa. c. The fused ventral outer wall of the aedeagus of male fleas.