Biochemical Divergence Between Cavernicolous and Marine
The position of crustaceans within Arthropoda - Evidence from nine molecular loci and morphology GONZALO GIRIBET', STEFAN RICHTER2, GREGORY D. EDGECOMBE3 & WARD C. WHEELER4 Department of Organismic and Evolutionary- Biology, Museum of Comparative Zoology; Harvard University, Cambridge, Massachusetts, U.S.A. ' Friedrich-Schiller-UniversitdtJena, Instituifiir Spezielte Zoologie und Evolutionsbiologie, Jena, Germany 3Australian Museum, Sydney, NSW, Australia Division of Invertebrate Zoology, American Museum of Natural History, New York, U.S.A. ABSTRACT The monophyly of Crustacea, relationships of crustaceans to other arthropods, and internal phylogeny of Crustacea are appraised via parsimony analysis in a total evidence frame work. Data include sequences from three nuclear ribosomal genes, four nuclear coding genes, and two mitochondrial genes, together with 352 characters from external morphol ogy, internal anatomy, development, and mitochondrial gene order. Subjecting the com bined data set to 20 different parameter sets for variable gap and transversion costs, crusta ceans group with hexapods in Tetraconata across nearly all explored parameter space, and are members of a monophyletic Mandibulata across much of the parameter space. Crustacea is non-monophyletic at low indel costs, but monophyly is favored at higher indel costs, at which morphology exerts a greater influence. The most stable higher-level crusta cean groupings are Malacostraca, Branchiopoda, Branchiura + Pentastomida, and an ostracod-cirripede group. For combined data, the Thoracopoda and Maxillopoda concepts are unsupported, and Entomostraca is only retrieved under parameter sets of low congruence. Most of the current disagreement over deep divisions in Arthropoda (e.g., Mandibulata versus Paradoxopoda or Cormogonida versus Chelicerata) can be viewed as uncertainty regarding the position of the root in the arthropod cladogram rather than as fundamental topological disagreement as supported in earlier studies (e.g., Schizoramia versus Mandibulata or Atelocerata versus Tetraconata).
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