galeaspid

Galeaspids were an extinct group of jawless fish that lived during the Silurian period. They are characterized by their flattened bodies and a large, protective bony shield that covered their heads and gills. This shield was a distinctive feature, often referred to as a "galea," which means helmet in Latin, giving the group its name.

These ancient fish were bottom-dwellers, likely feeding on organic matter found in the sediment. Their mouths were positioned ventrally, on the underside of their heads, and lacked jaws. Instead, they had a series of gill openings protected by the cranial shield. The exact structure and function of their sensory organs are still debated among paleontologists, but evidence suggests they had eyes.

Galeaspids are primarily known from fossils found in Asia, particularly in China. They represent an early and diverse lineage of armored agnathans, showcasing a unique evolutionary path in the development of vertebrate armor. Their ecological role and the specific reasons for their extinction remain areas of ongoing research. The group is considered important for understanding the early evolution of vertebrates and the diversification of jawless fish.