ostracoderm

from WordNet (r) 3.0 (2006)

ostracoderm
    n 1: extinct fish-like jawless vertebrate having a heavily
         armored body; of the Paleozoic

from The Collaborative International Dictionary of English v.0.48

ostracoderm \ostracoderm\ n.
   Any of several extinct fishlike jawless vertebrates having a
   heavily armored body; of the Paleozoic.
   [WordNet 1.5]