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 . 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
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 to consider the Olenellinae as sister group to the Chelicerata has been refuted, which contraposed many synapomorphies uniting them to the Trilobita instead.
Synonyms include Arachnata Paulus, 1979 and Palaeopoda Packard 1903.
Arachnomorpha Lameere 1890 [= Arachnata Paulus, 1979, = Palaeopoda Packard 1903]