cyclostomata

from The Century Dictionary.

• A division of gymnolæmatous polyzoans having tubular cells, partially free or entirely connate, a terminal opening with a movable lip, and no avicularia nor vibracula: opposed to Chilostomata and Ctenostomata. It is subdivided into Articulata or Radicata (family Crisiidœ), and Inarticulata or Inculatata, containing the rest of the families.
• In Günther's system of classification, a subclass of fishes having the following technical characters: the skeleton cartilaginous and notochordal, without ribs and without real jaws; skull not separate from the vertebral column; no limbs; gills in the form of fixed sacs without branchial arches, 6 or 7 in number on each side; one nasal aperture only; mouth circular or sucker-like; and heart without bulbus arteriosus. Also called Cyclostomi, Cyclostomia, Marsipobranchii, and Monorhina.

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

• noun plural (Zoöl.) A division of Bryozoa, in which the cells have circular apertures.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun primitive jawless aquatic vertebrate: lampreys; hagfishes