Galeaspida (galeaspids) are an extinct taxon of jawless marine fish and a subgroup of the Cephalaspidomorphi, which are itself a subgroup of the vertebrate. They lived in Silurian and Devonian times (430 to 370 million years ago). All fossils were found in Asia. Galeaspids are separated in Eugaleaspidiformes and Polybranchiaspidida. The name Galeaspida is derived from a latin word for helmet, galea. This refers to their massive bone shield on the head. Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ...
Some biologists no longer use the name Cephalaspidomorphi because relations among osteostraci and anaspida are unclear, and the affinities of the lampreys are also contested.
Others have restricted the cephalaspidomorphs to include only groups more clearly related to the Osteostraci, such as Galeaspida and Pituriaspida, that were largely unknown in the 1920s.
Many reference works still regard Cephalaspidomorphi as a Linnean class whose sole living representaties are the lampreys.
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