cleithra

Noun

cleithrum (plural cleithra)

1. A large bone in fishes, which extends upward from the base of the pectoral fin and anchors to the cranium above the gills, forming the posterior edge of the gill chamber.
   • The secondary arch consists of four pieces of bone, the posttemporal, supracleithrum, cleithrum and postcleithrum.[…]The cleithrum is the largest piece and the other elements are attached to it.1993, J. J. Videler, Fish Swimming, Springer, page 66