Aglaspidida is an extinct order of aquatic arthropods that were once regarded as primitive

chelicerate The subphylum Chelicerata (from New Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks, and mite ...

s. However, anatomical comparisons demonstrate that the aglaspidids cannot be accommodated within the chelicerates, and that they lie instead within the Artiopoda, thus placing them closer to the trilobites. Aglaspidida contains the subgroups Aglaspididae and Tremaglaspididae, which are distinguished by the presence of acute/spinose genal angles and a long spiniform tailspine in the Aglaspididae. Aglaspidid fossils are found in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

(upper Mississippi valley, Missouri and Utah), Europe,

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

, and

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

. Certain other artiopods are believed to be closely related to the aglaspidids, including the order Strabopida, which includes the

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

Strabops ''Strabops'' is a genus of strabopid, an extinct group of arthropods. ''Strabops'' is known from a single specimen from the Late Cambrian (Furongian age) of the Potosi Dolomite, Missouri, collected by a former professor, Arthur Thacher. It is ...

'', ''

Paleomerus ''Paleomerus'' is a genus of strabopid, a group of extinct arthropods. It has been found in deposits from the Cambrian period (Atdabanian epoch). It is classified in the family Strabopidae of the monotypic order Strabopida. It contains two ...

'', ''

Parapaleomerus ''Parapaleomerus'' is a genus of strabopid of small size found in Chengjiang biota, China. It contains one species, ''P. sinensis''. Unlike the other members of Strabopida, ''Parapaleomerus'' lacks dorsal eyes and only possesses ten trunk tergit ...

'', and possibly ''

Khankaspis ''Khankaspis'' is a poorly preserved arthropod genus that contains one species, ''K. bazhanovi'', recovered from the Snegurovka Formation of Siberia, Russia. Some authors have placed ''Khankaspis'' within the order Strabopida, but poorly preser ...

''.

List of genera

*'' Aglaspella'' *''

Aglaspis ''Aglaspis'' is the type genus of the family Aglaspididae within the arthropod order Aglaspidida. It lived on the seafloor in what is now Wisconsin during late Cambrian times. References External links ''Aglaspis''at the Paleobiology Databas ...

'' *''

Aglaspoides ''Aglaspoides'' is an extinct genus of aglaspid arthropod. External links ''Aglaspoides''at the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, pla ...

'' *''

Australaglaspis ''Australaglaspis stoneyensis'' is an aglaspid that superficially resembles a horseshoe crab, or trilobite. It is known from Idamean-aged strata (Late Cambrian) at Stoney Point in north-west Tasmania ) , nickname = ...

'' *'' Beckwithia'' *'' Chlupacaris'' *'' Chraspedops'' *''

Cyclopites ''Cyclopites'' is a genus of aglaspidid arthropods that lived in shallow seas in what is now Wisconsin during Late Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, a ...

'' *'' Flobertia'' *'' Girardevia'' *'' Glypharthrus'' *''

Kwanyinaspis ''Kwanyinaspis'' is a genus of arthropod from the Cambrian aged Chengjiang biota of Yunnan, China. It was described in 2005 based on a single specimen, ELI-2004001. Around 6 cm long, It has twelve trunk tergites with well developed posterior ...

'' *'' Quasimodaspis'' *'' Setaspis'' *'' Tremaglaspis'' *'' Tuboculops'' *'' Uarthrus'' *'' Zonoscutum'' *'' Zonozoe''

References

*Hesselbo, SP. 1992. Aglaspidida (Arthropoda) from the Upper Cambrian of Wisconsin. Journal of Paleontology 66(6)885-923. *Raasch, GO. 1939. Cambrian Merostomata. Geological Society of America Special Paper 19, 146p.

External links

Virtual fossli museum on AglaspidaMerostomata genera
Prehistoric arthropod orders Miaolingian first appearances Late Ordovician extinctions {{paleo-arthropod-stub