Arachnomorpha

Arachnomorpha; Temporal range:
	Fossil of Bellacartwrightia calliteles, a trilobite
	Lychas variatus, a scorpion chelicerate
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Clade:	Arachnomorpha; Lameere, 1890
Subgroups
	†Artiopoda; †Megacheira; ?†Marrellomorpha; Chelicerata;
Synonyms
	Arachnata Paulus, 1979; Palaeopoda Packard, 1903;

Arachnomorpha is a proposed subdivision or clade of Arthropoda, comprising the group formed by the trilobites and their close relatives (Artiopoda), Megacheira (which may be paraphyletic) and chelicerates. Under this proposed classification scheme, Arachnomorpha is considered the sister group to Mandibulata (including insects, crustaceans and myriapods).[1]

The arachnomorph concept has been challenged by suggestions that the artiopods are more closely related to mandibulates, forming the clade Antennulata instead.[2][1]

There is no consensus as to assigning Arachnomorpha a formal Linnean rank.

Classification

Arachnomorpha Lameere, 1890 [= Arachnata Paulus, 1979, = Palaeopoda Packard, 1903]

†Nettapezoura
†Dicranocaris
†Trilobita Walch, 1771
†Megacheira Hou & Bergstrom, 1997
†Strabopida Hou & Bergström, 1997
†Aglaspida Walcott, 1911
†Cheloniellida Broili, 1932
Chelicerata Heymons 1901
- Family †Sanctacarididae Legg & Pates, 2017
- Class Pycnogonida Latreille, 1810
- Clade Euchelicerata Weygoldt & Paulus, 1979
  - Family †Offacolidae Sutton et al., 2002
  - Clade Prosomapoda Lamsdell, 2013

Phylogeny

Using fossil data, Bergström & Hou (2003) gave an outline of arthropod relationships emphasizing trilobitomorphs (a group that includes trilobites and trilobite-like animals).[3]

Arthropods

Arachnomorpha

Limulavida

Sidneyia

	Aglaspidida

	Chelicerates

	Cheloniellon

Trilobitomorpha (s.s.)

Marrellomorpha

Acercostraca

Vachonisia

Marellida

	Mimetaster

	Marrella

Emeraldellida

Emeraldella

Retifaciida

Retifacies

Core trilobitomorphs

Concilioterga
Order Helmetiida

Helmetia

Kuamaia

	Sapenion

	Tegopelte

Nectopleura (e.g. Nektaspida)

Naraoia

Petalopleura
Order Xandarellida

Cindarella

	Xandarella

	Phytophilaspis

Trilobites, subclass Trilobita

	Hexapoda

	Crustaceans

Yohoia

Canadaspis

Fuxianhuia

References

Aria, Cédric (2022-04-26). "The origin and early evolution of arthropods". Biological Reviews. 97 (5): 1786–1809. doi:10.1111/brv.12864. ISSN 1464-7931. PMID 35475316. S2CID 243269510.
Gerhard Scholtz & Gregory Edgecombe (2005). "Heads, Hox and the phylogenetic position of trilobites". Crustacea and Arthropod Relationships. CRC Press. pp. 139–165. CiteSeerX 10.1.1.130.2585.
Bergström, J. & Hou, X. G. (2003). "Arthropod origins" (PDF). Bulletin of Geosciences. 78 (4): 323–334. Archived from the original (PDF) on 2016-03-04. Retrieved 2014-03-03.

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[:0-1] Aria, Cédric (2022-04-26). "The origin and early evolution of arthropods". Biological Reviews. 97 (5): 1786–1809. doi:10.1111/brv.12864. ISSN 1464-7931. PMID 35475316. S2CID 243269510.

[2] Gerhard Scholtz & Gregory Edgecombe (2005). "Heads, Hox and the phylogenetic position of trilobites". Crustacea and Arthropod Relationships. CRC Press. pp. 139–165. CiteSeerX 10.1.1.130.2585.

[B&H2003-3] Bergström, J. & Hou, X. G. (2003). "Arthropod origins" (PDF). Bulletin of Geosciences. 78 (4): 323–334. Archived from the original (PDF) on 2016-03-04. Retrieved 2014-03-03.