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. metazoa. Evidence points to the protist phylum Choanoflagellata as the likely ancestral group for the metazoa.. Porifera. . . . metazoa. parazoa. Sponges at the base of the phylogenetic tree:. no true tissuescell totipotencywater canal systemspiculespinacoderm (epithelial-like layer but lacking basement membrane and intercellular junctions).
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