Which extinct agnathan groups had bony head shields?

Several extinct groups of jawless, armored vertebrates—collectively known as ostracoderms—possessed bony head shields to protect their heads and gills. These groups include:12

• Osteostraci: Characterized by a broad, bony head shield with dorsal eyes and a median nostril on top of the head.3
• Heterostraci: Their heads were covered by two large bony plates (one dorsal and one ventral) separated by smaller plates.3
• Galeaspida: Featured a broad, semicircular bony head shield, sometimes extending into a pointed snout.3
• Arandaspida: Possessed a head covered in two large bony plates, similar to heterostracans, but separated by small plates surrounding individual gill openings.3
• Astraspida: Their heads were covered with small, mushroom-shaped bony plates.3

These armored agnathans thrived during the Paleozoic Era, primarily between the Silurian and Devonian periods, before becoming extinct.123