With a name indicating a tenuous link to chordates and thus ultimately to ourselves, the hemichordates (“half-chordates”) are obscure marine creatures popularly known as acorn worms. Most live in burrows and are direct deposit feeders, meaning that they scuffle about in mud or sand, gathering whatever nutritional benefits are available. Often the only evidence of their presence is fecal castings at the burrow entrances.
Each acorn worm has a three-part body consisting of a large, somewhat bulbous proboscis, a short, narrow collar and a long, sac-like trunk. So delicate are these secretive animals that excavating complete specimens for study and description is very challenging!
Thanks to these factors, combined with the acorn worm’s small size, even a simple species tally—five to eight for the Pacific Northwest—is only a guess. Of that number, only one has been scientifically documented and properly described.

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Acorn Worms