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Beardworms are slim, wormlike, deep-sea creatures so named for the thick cluster of long, fine, hairlike tentacles projecting from the front of the first section of a three-segmented body. There are approximately 120 species of beardworms, which belong to the phylum Pogonophora-from the Greek pogon, meaning beard, and phoron, meaning bearer.

The front section of the beardworm's body, which bears the tentacles, is quite short. The beardworm builds a protective tube around its entire body with mucus secreted from special glands in this body segment. As the worm grows (some beardworms reach a length of 5 ft [1.5 m]), the tube lengthens at either end and takes on the appearance of a series of ringed sections. Visible around the worm's long narrow trunk are hundreds of tiny projections—special glands that also secrete mucus, enabling the creature to move around in its protective tube. Following behind the trunk is the third, shorter section of the body, which is segmented and breaks off easily.

Beardworms have no mouth or intestines; instead, the blood-rich tentacles—as many as 200,000 on a giant beardworm of the genus Riftia—absorb all the nutrients the worm needs directly from the water. The tentacles of the female also serve a reproductive function. Although the species contains both sexes, beardworms do not mate because they never venture from their protective tube. Instead, the male releases tiny parcels of sperm that the female captures in her tentacles. Once the packet dissolves, the sperm are released inside the tube of the female where egg fertilization takes place.

Living on the ocean floor at depths ranging from approximately 330 ft (100 m) to more than tens of thousands of feet, beardworms burrow into the sea bed, often leaving only their front section projecting above the surface.

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