Doryaspis

Doryaspis (from Greek: δόρῠ dóru 'spear' and Greek: ἀσπίς aspís 'shield') (also known by its synonym, "Lyktaspis") is an extinct genus of primitive jawless fish that lived in the Devonian period. Fossils have been discovered in Spitsbergen.

Doryaspis Temporal range: Early Devonian PreꞒ Ꞓ O S D C P T J K Pg N
D. arctica fossils (MNHN.F.SVD653-655) at the National Museum of Natural History, France
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Infraphylum:	Agnatha
Class:	†Pteraspidomorpha
Subclass:	†Heterostraci
Order:	†Pteraspidiformes
Family:	†Protopteraspididae
Genus:	†Doryaspis White 1935
Type species
Doryaspis nathorsti (Lankester 1884) White 1935
Species
D. arctica Pernègre 2002 D. groenhorgensis Pernègre 2005 D. minor (Heintz 1960) D. nathorsti (Lankester 1884) White 1935
Synonyms
Scaphaspis Lyktaspis Heintz 1968

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 (that would correspond to the lower lip or chin in gnathostomes) 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.

• 
  Reconstruction of recently discovered species, D. arctica
• 
  Reconstruction of the type species, D. nathorsti
• 
  Reconstruction of D. nathorsti

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.^[1] However, several papers have incorrectly cited this study as supporting burrowing ecology.^[2][3]