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When and how did the mechanisms controlling regional identity in the vertebrate neural tube arise during evolution? The anatomy and embryology of the major deuterostome phyla (echinoderms, hemichordates, chordates) suggest that a true neural tube with dorsoventral and mediolateral regionalization arose with the chordates. We suggest that this was intimately(More)
The chaetognaths, or arrowworms, constitute a small and enigmatic phylum of marine invertebrates whose phylogenetic affinities have long been uncertain. A popular hypothesis is that the chaetognaths are the sister group of the major deuterostome phyla: chordates, hemichordates, and echinoderms. Here we attempt to determine the affinities of the chaetognaths(More)
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