Aglaspidida is an extinct order of aquatic
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
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 ...
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 (upper Mississippi valley,
Missouri
Missouri is a state in the Midwestern region of the United States. Ranking 21st in land area, it is bordered by eight states (tied for the most with Tennessee): Iowa to the north, Illinois, Kentucky and Tennessee to the east, Arkansas t ...
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 it ...
),
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 entirel ...
,
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 ''
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