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, ...

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 ...

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 A ...

s and a long spiniform tailspine in the Aglaspididae. Aglaspidid fossils are found in North America (upper Mississippi valley,

Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...

and

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

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 subcontinent of Eurasia and it is located enti ...

, Australia, and China. 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 ...

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'', ''

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'' *'' 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