''Doryaspis'' (from el, δόρῠ 'spear' and el, ἀσπίς 'shield') (also known by its synonym, "''Lyktaspis''") is an extinct genus of primitive

jawless fish Agnatha (, Ancient Greek 'without jaws') is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species. Among recent animals, cyclostomes ...

that lived in the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

period. Fossils have been discovered in

Spitsbergen Spitsbergen (; formerly known as West Spitsbergen; Norwegian: ''Vest Spitsbergen'' or ''Vestspitsbergen'' , also sometimes spelled Spitzbergen) is the largest and the only permanently populated island of the Svalbard archipelago in northern Norw ...

. 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. File:Doryaspis_arctica.JPG, Reconstruction of recently discovered species, ''D. arctica'' File:Doryaspis.jpg, Reconstruction of the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

, ''D. nathorsti''

Palaeoecology

Due to its unusual form, its ecology is debated. There are two hypotheses about lifestyle, to make it a surface

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

swimmer or a

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

burrower. For pelagic lifestyle, it mostly used its caudal fin to move. Fin-shaped plates may had effect of levitation by increasing the bearing surface of it. Water flows ejected by their gill openings may worked to stabilize and control lateral movements. On the other hand, benthic burrowing hypothesis is supported by its flat dorsal disc. Moving half-buried in the sediments allows it to filter nutrient particles. However, burrowing theory have problem, because gill openings are placed lower part of body, risking suffocation. Thus 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.

References

* THE GENUS DORYASPIS WHITE (HETEROSTRACI) FROM THE LOWER DEVONIAN OF VESTSPITSBERGEN, SVALBAR

* Long, John A. ''The Rise of Fishes: 500 Million Years of Evolution'', Baltimore: The Johns Hopkins University Press, 1996. Devonian jawless fish Pteraspidiformes genera Early Devonian fish of Europe Fossil taxa described in 1935 {{Pteraspidomorphi-stub