orbicula

noun2

1. •
   A dorsal sclerite over a hymenopteran arolium; a hard exoskeletal feature with species-specific shape that overhangs and protects the adhesive tip of such an insect's leg and around which the claw(s) curl. Abbreviation "or" or "rb".
2. •
   (old-fashioned) A discina (brachiopod).