Aglaspidida

Aglaspidida is an extinct order of aquatic arthropods that were once regarded as primitive chelicerates. However, anatomical comparisons demonstrate that the aglaspidids cannot be accommodated within the chelicerates,[2] and that they lie instead within the Artiopoda, thus placing them closer to the trilobites.[3] 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.[1]

Aglaspidida Temporal range:
Aglaspis spinifer
Fossil of Beckwithia typa
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
(unranked):	†Artiopoda
(unranked):	†Vicissicaudata
Order:	†Aglaspidida Walcott, 1911
Subtaxa[1]
†Australaglaspis †Beckwithia †Tremaglaspididae †Brachyaglaspis †Chlupacaris †Cyclopites †Flobertia †Quasimodaspis †Tremaglaspis †Aglaspididae †Aglaspella †Aglaspis †Aglaspoides †Chraspedops †Glypharthrus †Gogglops †Hesselbonia †Setaspis †Tuboculops †Uarthrus

Aglaspidid fossils are found in North America (upper Mississippi valley, Missouri and Utah), Europe, Australia, and China. Certain other artiopods are believed to be closely related to the aglaspidids, including the order Strabopida, which includes the genera Strabops, Paleomerus, Parapaleomerus, and possibly Khankaspis.