Ichthyological terms, not general ones.
One of the dermal, bony (sometimes cartilaginous), bilaterally paired, flattened struts inserting on the epihyal and/or ceratohyal (sometimes the interhyal and hypohyal) that supports the branchiostegal membranes.
Used in 4 profiles
The membrane, sometimes referred to as the gill membrane, connecting the branchiostegal rays and enclosing the ventral portion of the branchial cavity. Normally extended when the opercle of a fish is open, sealing the branchial cavity and creating a vacuum in the mouth, and also used during threat, courtship and other communicative behaviours in many species.
Used in 5 profiles
Either of the second pair of pharyngeal or gill arches. Supports part of the tongue and the branchiostegal rays.