| 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. |
| acorn worm n. Any of a class (Enteropneusta) of hemichordate, wormlike animals that inhabit shallow burrows in mud or sand flats of intertidal zones and are equipped with an acornlike proboscis used for digging and collecting food. |
acorn worm
any of the soft-bodied invertebrates of the class Enteropneusta, phylum Hemichordata. The front end of these animals is shaped like an acorn, hence their common name. The "acorn" consists of a proboscis and a collar that may be used to burrow into soft sand or mud. The animals vary in length from about 5 cm (about 2 inches) in certain Saccoglossus species to more than 180 cm (about 6 feet) in Balanoglossus gigas.
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