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Hemicyclaspis is an extinct genus of primitive jawless fish, closely related to Cephalaspis, was a genus of armored goldfish-sized to trout-sized detritivorous fish that lived in freshwater streams and estuaries of early Devonian Western Europe, that lived in the Devonian period.

Hemicyclaspis had a heavily armored, shovel-shaped headshield. This osteostracan meaning extinct jawless fish of the Devonian with armored head was a more powerful swimmer and could carry itself better in the water than either of its bottom dwelling relatives Dartmuthia or Tremataspis.

It had a dorsal fin which stabilized its body. whereas a pair of flaps covered with scales, like pectoral fins provided uplift to the body.

The corners of the head shield were drawn out into keel-like cutwaters and the enlarged upper lobe of the tail produced lift at the rear of the body. this kept the head of the fish down while it sucked up food from the seabed.