a large plate with a central "blister" is attached to the rear edge of the anterior cephalic doublure, typically the anterior edge of the hypostome lies directly under the anterior edge of the glabella

a piece of exoskeleton on the venter (underside) of the cephalon, thought of as a mouthpart. Typically the anterior edge of the hypostome lies directly under the anterior edge of the glabella.

Most apical region in hydra, surrounding the mouth opening.

The lower lip of trilobites, crustaceans, etc.