Doryaspis
Doryaspis is an extinct genus of primitive jawless fish that lived in the Devonian period. Fossils have been discovered in Spitsbergen.
The animals had canteen-shaped body armor and had large branchial plates that extended out and curved downward in a triangular shape, very similar to those of the pycnosteids. An element of the median oral plates extends out in a long rod-shaped appendage, called the "pseudorostrum." The tail is long and slender and has large rows of thick scales.
In the type species, D. nathorsti, the lateral edges of the branchial plates and of the pseudorostrum are serrated. The second species, D. arctica, is smaller, and lacks serrated edges.
Palaeoecology
Due to its unusual form, its ecology is debated. There are two hypotheses about lifestyle, whether it was a surface pelagic swimmer or a benthic burrower. For a pelagic lifestyle, it would have mostly used its caudal fin to move. Fin-shaped plates may have affected its buoyancy by increasing the bearing surface of it. Water flows ejected by their gill openings may have worked to stabilize and control lateral movements. On the other hand, the benthic burrowing hypothesis is supported by its flat dorsal disc. Moving half-buried in the sediments would have allowed it to filter nutrient particles. However, the burrowing theory has problems due to the gill openings being placed on the lower part of body, risking suffocation. This study in 2005 concluded that pelagic theory is more supported than burrowing theory. However, several papers have incorrectly cited this study as supporting burrowing ecology.