Aglaspidida is an extinct order of aquatic

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s 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 The Artiopoda is a grouping of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilo ...

, thus placing them closer to the

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

s. Aglaspidida contains the subgroups Aglaspididae and Tremaglaspididae, which are distinguished by the presence of acute/spinose

genal angle Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

s 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,

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and

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Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

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, 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 Strabopidae is the only family of the order Strabopida, a group of arachnomorph arthropods. The order Strabopida contains three valid genera and one doubtful, ''Khankaspis'', '' Paleomerus'', '' Parapaleomerus'' and '' Strabops'', all assigned in ...

, 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'', ''

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'', and possibly '' Khankaspis''.

List of genera

*'' Aglaspella'' *'' Aglaspis'' *'' Aglaspoides'' *'' Australaglaspis'' *'' Beckwithia'' *'' Chlupacaris'' *'' Chraspedops'' *'' Cyclopites'' *'' Flobertia'' *'' Girardevia'' *'' Glypharthrus'' *'' Kwanyinaspis'' *'' 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