: a phylum of invertebrates that has persisted with reduced numbers from the Lower Cambrian to the present and that consists of sedentary unsegmented marine animals with well-developed coelom and hemocoel, a lophophore, and often a fleshy stalk extending into the substrate, the body being enclosed in a bivalve chitinophosphatic or calcareous shell the valves of which are unequal, bilaterally symmetrical, and usually regarded as dorsal and ventral
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Merriam-Webster unabridged
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