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March 31 Ch 16 In all phyla except for sponges the embryonic ball of cells called a blastula folds in on itself forming a gastrula 1 Ectoderm 2 Mesoderm middle 3 Endoderm Protostome first mouth Deuterstome 2nd mouth anus first Sponges branch off early and extensive branch off method Oldest known sponge pushes back date for key split in evolution Resembles sac perforated with holes Draws water into central cavity Filter feeders 1 cm to 2 m across Cnidarians Box jellyfish most poisonous animal in world
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