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).

The arachnomorph concept has been challenged by suggestions that the artiopods are more closely related to mandibulates, forming the clade Antennulata instead.

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

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).

Arthropods Arachnomorpha Limulavida Sidneyia Aglaspidida Chelicerates Cheloniellon Trilobitomorpha (s.s.) Marrellomorpha Acercostraca Vachonisia Marrellida 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
ArthropodsArachnomorpha Limulavida Sidneyia Aglaspidida Chelicerates Cheloniellon Trilobitomorpha (s.s.) Marrellomorpha Acercostraca Vachonisia Marrellida 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
ArachnomorphaLimulavida Sidneyia Aglaspidida Chelicerates Cheloniellon Trilobitomorpha (s.s.) Marrellomorpha Acercostraca Vachonisia Marrellida 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
Limulavida Sidneyia Aglaspidida Chelicerates Cheloniellon
LimulavidaSidneyia
Aglaspidida Chelicerates Cheloniellon
Aglaspidida
Chelicerates
Cheloniellon
Trilobitomorpha (s.s.)Marrellomorpha Acercostraca Vachonisia Marrellida 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
MarrellomorphaAcercostraca Vachonisia Marrellida Mimetaster Marrella
AcercostracaVachonisia
MarrellidaMimetaster Marrella
Mimetaster
Marrella
EmeraldellidaEmeraldella
RetifaciidaRetifacies
Core trilobitomorphsConcilioterga Order Helmetiida Helmetia Kuamaia Sapenion Tegopelte Nectopleura (e.g. Nektaspida) Naraoia Petalopleura Order Xandarellida Cindarella Xandarella Phytophilaspis Trilobites, subclass Trilobita
Concilioterga Order HelmetiidaHelmetia Kuamaia Sapenion Tegopelte
Helmetia
Kuamaia
Sapenion Tegopelte
Sapenion
Tegopelte
Nectopleura (e.g. Nektaspida)Naraoia
Petalopleura Order XandarellidaCindarella Xandarella Phytophilaspis
Cindarella
Xandarella Phytophilaspis
Xandarella
Phytophilaspis
Trilobites, subclass Trilobita
Hexapoda Crustaceans Yohoia Canadaspis Fuxianhuia
Hexapoda Crustaceans Yohoia
Hexapoda Crustaceans
Hexapoda
Crustaceans
Yohoia
Canadaspis
Fuxianhuia