Nektaspida is an extinct order of non-mineralised artiopodan arthropods. They are known from the lower-Cambrian to the upper Silurian. Originally classified as trilobites, which they superficially resemble, they are now placed as close relatives as members of the Trilobitomorpha within Artiopoda. The order is divided into three major families; Emucarididae, Liwiidae, and Naraoiidae.
Sidneyia is an extinct marine arthropod known from fossils found from the Early to the Mid Cambrian of China and the Mid Cambrian Burgess Shale of British Columbia, Canada.
Cheloniellida is a taxon of extinct Paleozoic arthropods. As of 2018, 7 monotypic genera of cheloniellids had been formally described, whose fossils are found in marine strata ranging from Ordovician to Devonian in age. Cheloniellida has a controversial phylogenetic position, with previous studies associated it as either a member or relative of various fossil and extant arthropod taxa. It was later accepted as a member of Vicissicaudata within Artiopoda.
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, 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.
Kerygmachela kierkegaardi is a kerygmachelid gilled lobopodian from the Cambrian Stage 3 aged Sirius Passet Lagerstätte in northern Greenland. Its anatomy strongly suggests that it, along with its relative Pambdelurion whittingtoni, was a close relative of radiodont and euarthropods. The generic name "Kerygmachela" derives from the Greek words Kerygma (proclamation) and Chela (claw), in reference to the flamboyant frontal appendages. The specific name, "kierkegaardi" honors Danish philosopher Søren Kierkegaard.
Urokodia is an extinct genus of arthropod from the early Cambrian. The only known species is Urokodia aequalis from the Maotianshan Shales of China based on some 15 specimens.
Megacheira is an extinct class of predatory arthropods defined by their possession of spined "great appendages". Their taxonomic position is controversial, with studies either considering them stem-group euarthropods, or stem-group chelicerates. The homology of the great appendages to the cephalic appendages of other arthropods is also controversial. Uncontested members of the group were present in marine environments worldwide from the lower Cambrian to the upper Ordovician.
This is a list of fossils found at Maotianshan Shales, whose most famous assemblage of organisms are referred to as the Chengjiang biota.
Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a variety of functions. Radiodonts were among the earliest large predators, but they also included sediment sifters and filter feeders. Some of the most famous species of radiodonts are the Cambrian taxa Anomalocaris canadensis, Hurdia victoria, Peytoia nathorsti, Titanokorys gainesi, Cambroraster falcatus and Amplectobelua symbrachiata. The later surviving members include the subfamily Aegirocassisinae from the Early Ordovician of Morocco and the Early Devonian member Schinderhannes bartelsi from Germany.
Emeraldella is a genus of arthropod known from the Middle Cambrian of North America. The type species E. brocki was described in 1912 from the Burgess Shale. 21 specimens of Emeraldella are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community. A re-study on the species was done in 2012. A second species E. brutoni is known from the Wheeler Shale, which was described in 2011. An additional specimen of E. brutoni was described in 2019, which revealed more of the anatomy. It has been placed as a basal member of the clade Vicissicaudata within Artiopoda, a group of arthropods containing trilobites and their relatives.
Mollisonia is an extinct genus of Cambrian arthropod. 4 species had been described from North America and China. Studies suggest it is a basal member of Chelicerata, a group which includes horseshoe crabs and arachnids.
The Marjum Formation is a Cambrian geological formation that overlies the Wheeler Shale in the House Range, Utah. It is named after its type locality, Marjum Pass, and was defined in 1908. The formation is known for its occasional preservation of soft-bodied tissue, and is slightly younger than the Burgess Shale, falling in the Ptychagnostus praecurrens trilobite zone.
Thelxiope is a genus of Cambrian and Ordovician arthropod. Four named species are known, the type species T. palaeothalassia is known from the Burgess Shale, Canada T. holmani is from the Wheeler Shale of Utah, Thelxiope tangi from the Linyi Lagerstätte of Shandong, China, and T. spinosa, which is known from both the Linyi Lagerstätte and the Wheeler Shale. An indeterminate species is also known from the Ordovician (Floian) Fezouata Formation in Morocco. It is a member of Mollisoniida, alongside close relatives Mollisonia and Corcorania. They are suggested to be stem-chelicerates.
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 Trilobitomorpha. Trilobites, in part due to abundance of findings owing to their mineralized exoskeletons, are by far the best recorded, diverse, and long lived members of the clade. Other members, which lack mineralised exoskeletons, are known mostly from Cambrian deposits.
Falcatamacaris is an extinct genus of Cambrian artiopodan arthropod, only known from the type species F. bellua described in 2014, from the Guzhangian aged Weeks Formation in Utah. The holotype specimen is over 10 cm long. The trunk consists of 11 tergites, with crescent shaped pleural spines. Its placement within the Artiopoda was unresolved.
Cheloniellon is a monotypic genus of cheloniellid arthropod, known only by one species, Cheloniellon calmani, discovered from the Lower Devonian Hunsrück Slate of Germany.
Vicissicaudata is an unranked group of artiopods, containing Cheloniellida, Aglaspidida and several other genera outside these groups like Sidneyia and Emeraldella.
Pseudoarctolepis is an extinct genus of bivalved arthropod known from the Cambrian period. The type species, P. sharpi was described by Brooks & Caster in 1956 from specimens found in the Wheeler Shale of Utah. It is unusual among Cambrian arthropods for having a pair of wing-like structures projecting outwards from the carapace. A second species, P. semicircularis has been described from the Kaili Biota in South China, which differs from the type species in the fact that the wings are semicircular rather than blade-like. A possible related form has been reported from the Ordovician of Portugal. They were relatively large, with some carapaces of P. sharpi reaching 11 centimetres (4.3 in) in length. The soft-bodied anatomy is poorly known, though the poorly preserved posterior anatomy of a specimen of P. sharpi is known, which consists of a narrow segmented abdomen, which ends with a pair of caudal rami. They are thought to have been actively swimming nektonic organisms. Affinities to the bivalved arthropod group Hymenocarina have been proposed, but the limited knowledge of the anatomy makes the referral tentative.
Habeliida is an order of extinct arthropods that existed during the middle Cambrian. It is divided into two families, Habeliidae, and Sanctacarididae. They are thought to have been durophagous, with robust gnathobases used to shred hard-shelled organisms. Remains of trilobites have been found as stomach contents in Wisangocaris. Messorocaris has been suggested to be part of the order in some studies, but this is uncertain. They are suggested to be stem-group chelicerates, though they lack the chelicerae present in true chelicerates.
Notchia weugi is a species of enigmatic arthropod from the Weeks Formation of Utah. It is the only species in the genus Notchia.
