anaspida

from The Century Dictionary.

• An ordinal term introduced by Traquair for a group of singular fishes, chiefly from the Upper Silurian rocks of Lanarkshire, without paired fins and having a tubereled skin, a heterocercal tail, and a row of prominent processes along the belly.

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

• noun extinct order of jawless vertebrates