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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.

Subjects: Genetics and Genomics — Zoology and Animal Sciences.

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