subopercular

from The Century Dictionary.

• Composing a lower part of the operculum or gill-flap of a fish; pertaining to a suboperculum in any sense, or having its character. See cut under opercular.
• noun In ichthyology, the suboperculum.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Anat.) Situated below the operculum; pertaining to the suboperculum.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective anatomy Situated below the operculum.
• adjective anatomy Relating to the suboperculum.
• noun anatomy The suboperculum.