Galeaspida

The Galeaspida were an extinct order of primitive, jawless vertebrates that lived during the Early Silurian to Late Devonian periods (approximately 443.8 to 358.9 million years ago). They are characterized by a broad, semicircular head shield, which in some species was drawn out into a pointed snout. Their eyes were located on the dorsal side of the head, and they possessed a large, median nostril. The gills of Galeaspida were situated on the underside of the head. This group is part of the larger category of ostracoderms, which were among the earliest vertebrates. Galeaspida are known from numerous species and are divided into two major clades: Polybranchiaspidida and Eugaleaspidiformes.12