Opercular

noun

1. The upper posterior bone of the series of bones forming the gill-cover in fishes.
2. Of or pertaining to an operculum or opercle.
3. Having an operculum; fitted with or closed by an operculum; operculate.
4. one bounding the operculum below and more or less behind: the suboperculum
5. one between the suboperculum and the operculum on the one hand and the preoperculum in front: the interoperculum, which is connected by a ligament with the lower jaw; and