hypostomata

from The Century Dictionary.

• A superclass of extinct, fish-like vertebrates, the Ostracodermi of Cope and other writers: contrasted with Cyclostomata, the lampreys, and Gnathostomata, vertebrates with true jaws.
• An order or suborder of fishes, confined to the eastern seas, alone represented by the family Pegasidœ, of uncertain position, supposed to be related to the mail-cheeked series of acanthopterygians. Originally written in the French form Hypostomides by Duméril.
• A group of echinoderms.
• Infusorians in which the mouth is inferior or ventral.

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

• noun Plural form of hypostoma.