Arachnomorpha

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Arachnomorpha
Temporal range: Cambrian - Recent
Haeckel Arachnida.jpg
"Arachnida" from Ernst Haeckel's Kunstformen der Natur, 1904
Scientific classification e
Kingdom: Animalia
Phylum: Arthropoda
Clade: Arachnomorpha
Lameere, 1890
Synonyms
  • Arachnata Paulus, 1979
  • Palaeopoda Packard, 1903

Arachnomorpha is a subdivision or clade of Arthropoda, comprising the monophyletic group formed by the trilobites, other great appendage arthropods and trilobite-like families (Helmetiidae, Xandarellidae, Naraoiidae, Liwiidae, and Tegopeltidae), and a diverse sister clade including the chelicerates.[1][2] Great debate is held on the position of the Pycnogonida, which are currently thought not to be placed in the immediate vicinity of the Chelicerata.[3] Arachnomorpha are considered the sister group to the crustaceans, which are increasingly being accepted as members of the mandibulate clade (including insects and myriapods).[2]

The arachnomorph concept has been challenged by suggestions that the trilobites fall in the mandibulata stem-group.[4]

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

A proposal, which contraposed many synapomorphies uniting them to the Trilobita instead.[5] Consideration of the Olenellinae as sister group to the Chelicerata has been refuted.[6]

Classification[edit]

  • ?Pycnogonida Latreille, 1806 (incl. Pantopoda Gerstaecker, 1863)

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

Phylogeny[edit]

Using fossil data, Bergström & Hou (2003) gave an outline of arthropod relationships emphasizing trilobitomorphs (a group that includes trilobites and trilobite-like animals).[7]

Arthropods
Arachnomorpha
Limulavida

Sidneyia

Aglaspidida

Chelicerates

Cheloniellon

Trilobitomorpha (s.s.)
Marrellomorpha
Acercostraca

Vachonisia

Marellida

Mimetaster

Marrella

Emeraldellida

Emeraldella

Retifaciida

Retifacies

Crown group
 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[edit]

  1. ^ Trevor J. Cotton & Simon J. Braddy (2003). "The phylogeny of arachnomorph arthropods and the origin of the Chelicerata". Transactions of the Royal Society of Edinburgh: Earth Sciences. 94 (3): 169–193. doi:10.1017/S0263593300000596. 
  2. ^ a b Jonathan R. Hendricks & Bruce S. Lieberman (2008). "New phylogenetic insights into the Cambrian radiation of arachnomorph arthropods". Journal of Paleontology. 82 (3): 585–594. doi:10.1666/07-017.1. 
  3. ^ J. A. Dunlop & C. P. Arango (2005). "Pycnogonid affinities: a review". Journal of Zoological Systematics and Evolutionary Research. 43 (1): 8–21. doi:10.1111/j.1439-0469.2004.00284.x. 
  4. ^ Gerhard Scholtz & Gregory Edgecombe (2005). "Heads, Hox and the phylogenetic position of trilobites". Crustacea and Arthropod Relationships. CRC Press. pp. 139–165. CiteSeerX 10.1.1.130.2585Freely accessible. 
  5. ^ Karl-Ernst Lauterbach (1980). "Schlüsselereignisse in der Evolution des Grundplans der Arachnata (Arthropoda)" [Key events in the evolution of the ground plan of the Arachnata (Arthropoda)]. Abhandlungen des Naturwissenschaftlichen Vereins in Hamburg. NF (in German). 23: 163–327. 
  6. ^ R. A. Fortey & H. B. Whittington (1989). "The Trilobita as a natural group" (PDF). Historical Biology. 2: 125–138. doi:10.1080/08912968909386496. 
  7. ^ Bergström, J. & Hou, X. G. (2003). "Arthropod origins" (PDF). Bulletin of Geosciences. 78 (4): 323–334.