Ostracodermi (ostracoderms) The name often used in older textbooks for the fossil, armoured, jawless, agnathan fish of the Ordovician to early Carboniferous Periods. Probably the name indicates only a grade of development; some ostracoderms are close to the line of ancestry of the living Agnatha (lamprey and hagfish), others to the origin of the jawed vertebrates. The informal version of the name survives. See also CEPHALASPIDOMORPHI; PTERASPIDOMORPHI.

Ostracodermi (ostracoderms) The name often used in older textbooks for the fossil, armoured, jawless, agnathan fish of the Ordovician to early Carboniferous. Probably the name indicates only a grade of development; some ostracoderms are close to the line of ancestry of the living Agnatha (lamprey and hagfish), others to the origin of the jawed vertebrates. The informal version of the name survives.