Amphiaspidida is a taxon of extinct cyathaspidid heterostraci whose fossils are restricted to Lower Devonian marine strata of Siberia near the Taimyr Peninsula. Some authorities treat it as a suborder of Cyathaspidiformes,[Lundgren, Mette, and Henning Blom. "Phylogenetic relationships of the cyathaspidids (Heterostraci)." GFF 135.1 (2013): 74-84.] while others treat it as an order in its own right as " Amphiaspidiformes."[Novitskaya, Larisse. Les amphiaspides (Heterostraci) du Devonien de la Siberie. Éditions du Centre national de la recherche scientifique, 1971.] In life, they are thought to be benthic animals that lived most of their lives mostly buried in the sediment of a series of hypersaline lake. Amphiaspids are easily distinguished from other heterostracans in that all of the plates of the cephalothorax armor are fused into a single, muff-like unit, so that the forebody of the living animal would have looked like a potpie or a hot waterbottle with a pair of small, or degenerated eyes sometimes flanked by preorbital openings, a pair of branchial openings for exhaling, and a simple, slit-like, or tube-like mouth.
Taxonomy
Amphiaspidida is traditionally regarded as the sister-taxon or daughter-taxon of the cyathaspidid family
Ctenaspidae (ne "Ctenaspididae"), though no formal shared traits are identified between the two groups.
The ctenaspidid cyathaspid,
Boothiaspis, of Lower Devonian Canada, was initially described as an amphiaspid.
As mentioned earlier, Amphiaspidida is treated as either a suborder of Cyathaspidiformes, or as an order in its own right, sometimes referred to as "Amphiaspidiformes." Regardless of its own status, Amphiaspidida is divided into three superfamilies, Amphiaspidoidei, Hibernaspidoidei, and Siberiaspidoidei. An additional species, Gunaspis orientalis, is treated as Amphiaspidida incertae sedis because it is known only from fragments with distinctive micro-ornamentation.
Amphiaspidoidei
The superfamily Amphiaspidoidei contains four families.
Amphiaspididae
This family contains two monotypic genera, including the type genus
Amphiaspis, and
Amphoraspis
Edaphaspididae
This family is monotypic, and contains the monotypic genus
Edaphaspis.
Gabreyaspididae
This family contains four genera,
Gabreyaspis,
Prosarctaspis,
Pelaspis, and
Tareyaspis.
Olbiaspididae
This family contains three genera,
Olbiaspis,
Kureykaspis and
Angaraspis.
Hibernaspidoidei
This superfamily contains three families.
Hibernaspididae
This family is monotypic, containing only the genus
Hibernaspis.
Eglonaspididae
This is a diverse family that contains five genera, including
Eglonaspis,
Gerronaspis,
Lecaniaspis,
Empedaspis, and
Pelurgaspis.
Aphataspididae
This family contains two monotypic genera,
Aphataspis and
Putoranaspis.
Siberiaspidoidei
This superfamily contains two families,
Siberiaspididae, and
Tuxeraspididae.
Siberiaspididae
This family contains two monotypic genera,
Siberiaspis, and
Argyriaspis.
Tuxeraspididae
This family contains three monotypic genera,
Tuxeraspis,
Litotaspis, and
Dotaspis.
Tuxeraspis and
Litotaspis are known primarily from fragments and portions of the head-region, while
Dotaspis is known from a mostly intact headshield.
[Новицкая ЛИ (1986), "Древнейшие бесчелюстные СССР: Гетеростраки: Циaтacпиды, Aмфиacпиды, Птepacпиды." Труды ПИН 219: 159c. Novitskaya,]
