Arachnomorpha

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]

Arachnomorpha Temporal range: Cambrian - Recent PreꞒ Ꞓ O S D C P T J K Pg N
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

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

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