Biology:Artiopoda

Short description: Extinct group of arthropods

Artiopoda Temporal range: Early Cambrian - Late Permian PreЄ Є O S D C P T J K Pg N
Misszhouia, a nektaspid
Cheloniellon, a cheloniellid
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
(unranked):	†Artiopoda Hou and Bergstrom, 1997
Subgroupings
†Squamacula †Thulaspis Protosutura †Acanthomeridion †Zhiwenia †Australimicola †Campanamuta †Falcatamacaris †Molaria †Retifacies †Pygmaclypeatus †Bailongia †Strabopida? Trilobitomorpha †Retifacies? †Pygmaclypeatus? †Campanamuta? †Kwanyinaspis †Arthroaspis †Tonglaiia †Nektaspida †Trilobita †Agnostida(Traditionally included within Trilobita) †Conciliterga †Haifengella †Helmetia †Kuamaia †Kwanyinaspis †Rhombicalvaria †Saperion †Skioldia †Tegopelte †Xandarellida (=Petalopleura) †Luohuilinella †Cindarella †Phytophilaspis †Xandarella †Sinoburius †Zhugeia Vicissicaudata †Xenopoda (possibly paraphyletic) †Sidneyia †Emeraldella †Etania †Kodymirus †Eozetetes †Carimersa †Cheloniellida †Aglaspidida

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 their mineralising exoskeletons, are by far the most diverse and long lived members of the clade, with most records of other members, which lack mineralised exoskeletons, being from Cambrian deposits.

Description

Morphology of Cambrian artiopod Retifacies, showing the morphology of the limbs (E, F) Key for limb morphology: exopod (exo) exite (exi) protopodite (pt) podomere (pd) spine/setae (s) terminal claw (tc)

According to Stein and Selden (2012) artiopods are recognised by the possession of filiform antennulae, limbs with bilobate exopods, with the proximal lobe being elongate and bearing a lamella, while the distal lobe is paddle-shaped and setiforous (bearing hair-or bristle like structures). The limb endopod has seven podomeres/segments, with first four podomeres bearing inward facing (endite) structures, while podomeres five and six are stenopodous (cylindrical and stout). Common plesiomorphies also include the antellules and at least three sets of post-antellulae limbs being incorporated into the head shield, the postantennular limbs having no or little differentiation into distinct morphologies, and broad paratergal folds which contribute to the dorsoventrally flattened look of artiopods. The limbs of artiopods have also been suggested to bear exites, which were described as similar those of the megacheiran Leanchoilia and probably not homologous to those present in crustaceans.

Taxonomy

Internal taxonomy

The Artiopoda have been considered by many studies to consist of two major clades; one reusing Trilobitomorpha to encompass trilobites, nektaspids, concilitergans and xandarellids, and the other called Vicissicaudata encompassing aglaspidids, xenopods and cheloniellids. There are some taxa, such as Squamacula and the members of "Protosutura", which often are placed near the base of Artiopoda, outside the Vicissicaudata+Trilobitomorpha clade. These relationships are not always recovered.

Relationships with other arthropods

The relationship of Artiopoda with the two major clades of modern arthropods, the Chelicerata and the Mandibulata, are unresolved, with some phylogenies recovering Artiopoda as more closely to chelicerates, forming the clade Arachnomorpha, while others recover Artiopoda as more closely related to mandibulates, forming the clade Antennulata. Some studies place them as stem-group euarthropods, with mandibulates and chelicerates more closely related to each other than either is to Artiopoda. Some studies have recovered a close relationship with Marrellomorpha, with the proposed clade including Artiopoda and Marrellomorpha dubbed Lamellipedia, though this relationship is not found in other analyses. The enigmatic artiopodan-like arthropod Kiisortoqia, which bears large "frontal appendages" has been suggested to be closely related to Artiopoda in some analyses.

Gallery

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  Restoration of the trilobite Triarthrus eatoni

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  Fossils of Naraoia compacta (Nektaspida)

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  Life restoration of Sidneyia (Vicissicaudata)

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  Diagram of Sinoburius (Xandarellida)

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  Life restoration of Trimerus (Trilobita)

Phylogeny

After Jiao et al. 2021.

Artiopoda

Squamacula clypeata     Protosutura      Zhiwenia coronata     Australimicola spriggi         Acanthomeridion serratum     Acanthomeridion anacanthus           Bailongia longicaudata   Trilobitomorpha    Retifacies abnormalis           Kwanyinaspis maotiashanensis   Trilobita   Olenoides serratus     Eoredlichia intermedia       Conciliterga   Haifengella corona         Kuamaia lata     Helmetia expansa         Tegopelte gigas     Skioldia aldna     Saperion glumaceum             Xandarellida   Cindarella eucalla       Luohuilinella deletres     Luohuilinella rarus       Sinoburius lunaris       Xandarella spectaculum     Phytophilaspis pergamena           Nektaspida   Buenaspis forteyi       Tariccoia arrusensis     Soomaspis splendida     Liwia convexa         Naraoia spinosa       Naraoia compacta     Misszhouia longicaudata               Vicissicaudata    Sidneyia inexpectans       Emeraldella brocki   Cheloniellida   Cheloniellon calmani       Triopus draboviensis     Duslia insignis           Kodymirus vagans       Eozetetes gemmelli   Aglaspidida   Beckwithia typa         Chlupacaris dubia       Quasimodaspis brentsae       Tremaglaspis unite       Tremaglaspis vanroyi     Brachyaglaspis singularis             Cyclopites vulgaris     Australaglaspis stonyensis       Uarthrus instabilis     Flobertia kochi       Aglaspella granulifera       Gogglops ensifer       Glypharthrus simplex     Aglaspis spinifer           Chraspedops modesta       Glypharthrus thomasi       Glypharthrus trispinicaudatus     Glypharthrus magnoculus

References

Wikidata ☰ Q19842587 entry