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Deuterostomia The name sometimes given to a number of animal phyla (Chordata, Hemichordata, Pogonophora, Echinodermata, and Chaetognatha) thought by many to share a common ancestry. The name indicates the mode of formation of the mouth opening in embryogeny: the first embryonic opening (the blastopore) becomes the anus, and the second opening becomes the mouth. Compare PROTOSTOMIA.

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Xenoturbellida A phylum known by only a single species, Xenoturbella bocki, found in the N. Sea and described in 1949 by E. Westblad. It is up to 30 mm long, hermaphrodite, and ciliated (cilium); it has no anus, but is coelomate.