Marellomorpha The Lace Crabs

The extinct subphylum Marellomorpha consists of several enigmatic marine fossils from the Cambrian to Devonian, the most famous of which is Marella (the "lace crab") from the Burgess Shale (Wolcott, 1912), and is perhaps the most common nontrilobite arthropod in these deposits. Other genera include Mimetaster and Vachonisia. The lineage is supported as monophyletic based on four traits (Stürmer and Bergström, 1976; Wills et al., 1998): number of head appendages, large number of trunk somites, regular decrease in the length of the trunk appendages, and the division of the trunk endopods into five podomeres. Marellomorphs may be the sister group to Arachnomorpha (see discussion that follows) or basal within a larger grouping called Schizoramia, which also consists of Arachnomorpha but as the sister group of Crustaceomorpha (see debate concerning Schizoramia monophyly, later in this chapter).

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