Anaspida

thumb|254px|right|Anaspids are characterized by a large, tri-radiate spine (red) posteriorly to the series of branchial openings. It is assumed that the most primitive anaspids, such as Pharyngolepis (top), possessed a long, ribbon-shaped, [[ventrolateral fin-fold (green). More advanced forms, such as Rhyncholepis (bottom), possessed a shorter paired fin-fold (green) and enlarged, spine-shaped, median dorsal scutes. – Philippe Janvier]] Anaspida ("shieldless ones") is an extinct group of jawless fish that existed from the early Silurian period to the late Devonian period. They were classi