Arachnomorpha

Taxobox
name = Arachnomorpha

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image_width = 250px
image_caption = "Arachnida" from Ernst Haeckel's "Kunstformen der Natur", 1904
fossil_range = Cambrian - Present Day
regnum = Animalia
phylum = Arthropoda
unranked_classis = Arachnomorpha
subdivision_ranks =
subdivision =
*Trilobita Walch 1771
*Strabopida Hou & Bergström, 1997
*Aglaspida Walcott, 1911
*Cheloniellida Broili, 1932
*Chelicerata Heymons 1901
**Class Xiphosura Latreille, 1802
**Class Chasmataspida Caster & Brooks, 1956
**Class Eurypterida Burmeister, 1843
**Class Arachnida Lamarck, 1801

Arachnomorpha ("Spider Form") Lameere 1890 is a subdivision of Arthropoda, containing the monophyletic group formed by the trilobites and other trilobite-like families (Helmetiidae, Xandarellidae, Naraoiidae, Liwiidae, and Tegopeltidae, and a diverse sister clade including the chelicerates [Cotton, T.J., & Braddy, S.J. 2004. "Transactions of the Royal Society of Edinburgh: Earth Sciences", 94: 169–193] . 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 [Dunlop, J.A. & Arango, C.P. 2005. "Journal of Zoological Systematics and Evolutionary Research", 43: 8-21.]

There is no consensus as to assigning Arachnomorpha a formal Linnean category. It could be a Subphylum or a Superclass and then its subgroups Cheliceromorphora and Trilobita would be ranked as various infrataxa and the Chelicerata sensu stricto would be a Class.

A proposal [Lauterbach, K.E. 1980. "Abhandlungen des Naturwissenschaftlichen Vereins Hamburg" (NF), 23:163-327.] to consider the Olenellinae as sister group to the Chelicerata has been refuted [Fortey, R.A., & Whittington, H.B. 1989. "Historical Biology", 2:125–138.] , which contraposed many synapomorphies uniting them to the Trilobita instead.

Synonyms include Arachnata Paulus, 1979 and Palaeopoda Packard 1903.

Classification of the Arachnomorpha

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

Arachnomorpha Lameere 1890 [= Arachnata Paulus, 1979, = Palaeopoda Packard 1903]
*Trilobita Walch 1771
*Strabopida Hou & Bergström, 1997
*Aglaspida Walcott, 1911
*Cheloniellida Broili, 1932
*Chelicerata Heymons 1901 [= Euchelicerata Weygoldt & Paulus, 1979]
**Class Xiphosura Latreille, 1802
**Class Chasmataspida Caster & Brooks, 1956
**Class Eurypterida Burmeister, 1843
**Class Arachnida Lamarck, 1801

References