Kingdom Animalia Phylum Arthropoda | Scientific name Arachnomorpha Higher classification Arthropod | |
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Clade Arachnomorpha
Lameere, 1890 Lower classifications Chelicerata, Arachnid, Scorpion, Eurypterid, Xiphosura | ||
An introduction to arthropods presentation 2 arachnomorpha
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. 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. Arachnomorpha are considered the sister group to the crustaceans, which are increasingly being accepted as members of the mandibulate clade (including insects and myriapods).
Contents
The arachnomorph concept has been challenged by suggestions that the trilobites fall in the mandibulata stem-group.
There is no consensus as to assigning Arachnomorpha a formal Linnean rank.
A proposal, which contraposed many synapomorphies uniting them to the Trilobita instead. to consider the Olenellinae as sister group to the Chelicerata has been refuted.
Classification
Arachnomorpha Lameere, 1890 [= Arachnata Paulus, 1979, = Palaeopoda Packard, 1903]
Phylogeny
Using fossil data, Bergström & Hou (2003) gave an outline of arthropod relationships emphasizing trilobitomorphs (a group that includes trilobites and trilobite-like animals).