Galeaspida

Hanyangaspis (top), Lungmenshanaspis (center), Sanchaspis (bottom right), Eugaleaspis (bottom left)

• China
• Tibet
• North Vietnam

The Galeaspida are extinct jawless, fishlike vertebrates that lived in the Silurian and Devonian. Fossils of this very rich in forms group was found in China, Tibet and the north of Vietnam often deposited in coastal marine sediments, as well as in deposits of lagoons and estuaries. They were probably endemic in the region.

Features

The animals had a generally flattened body and an armored by a massive shield head. Front plate in the center of which was an opening shot using probably the breathing water flowed and odors. The eyes were far apart on the edge of the header tank. The typical for Osteostraci lateral sensory fields are missing, but the Galeaspida have an extensive system of sensory channels. The number of the side, resting on the bottom of gill holes was often very large, up to 24 on each side. And the mouth was on the underside. The rear body was covered with small scales. The shape of the rear body, including the tail, is largely unknown. Except for the tail fin, there were no fins.

System

Overall, about 70 Galeaspida species were scientifically described, the two Hauptkladen that Eugaleaspidiformes and Polybranchiaspidida ( " Polybranchiaspidiformes " Huananaspidiformes ) are assigned. Hanyangaspis, Dayongaspis and Xiushuiaspis are basal forms.

The Eugaleaspidiformes and Polybranchiaspidida are sister groups and have as a synapomorphy a single, transverse sensory channel. The three basal genera have two such channels as the Heterostraci and Thelodonti. The Eugaleaspidiformes have a horseshoe-shaped head shield and a slot- shaped mean basal opening. As basal Galeaspida they have only six to eight gill openings. The Polybranchiaspidida have a lot of gill openings (10 to 45). They are divided into the likely basal and paraphyletic " Polybranchiaspidiformes " who had an oval head tanks, and in the Huannanaspidiformes whose head shield was characterized by long lateral outgrowths.