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characteristics of an animal
-no cell wall
an embryonic stage that marks the end of cleavage during animal development; a hollow ball of cells in many species.
the embryonic stage resulting from gastrulation in animal development. most animals have a gastrula made up of three layers of cells: endoderm, ectoderm, and mesoderm
a skeletal system composed of fluid held under pressure in a closed body compartment; the main skeleton of most cnidarians, flatworms, nematodes, and annelids.
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