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Different scenarios for the evolution of morphology and larva of Xenoturbella. a, b Phylogenetic trees showing Xenacoelomorpha as an early-branching bilaterian. c, d Phylogenetic trees showing Xenacoelomorpha as a deuterostome. Black circles show gain and black crosses show loss of adult organs (e.g. coeloms and anus). White circles show gain and white crosses show loss of feeding planktotrophic larva
