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Meaning of acorn worm

a'corn worm"

Pronunciation: [key]
  1. any of several burrowing, often brilliantly colored hemichordates of the class Enteropneusta, usually found in intertidal sand and mud, having an acorn-shaped proboscis and collar.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.