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Pogonophora

Pogonophora (beard worms) A phylum comprising deep-sea worms, first encountered in early Cambrian rocks but discovered only in the 20th century. Beard worms bear a superficial resemblance to Polychaeta and it has recently been proposed that they are actually very highly specialized polychaetes. They live at great depths inside chitinous tubes they secrete for themselves in soft substrates, often in the vicinity of hydrothermal vents. The body is coelomate, partly segmented, has ‘bristles’ (chaetae), and is divided into three parts, the anterior crowned with tentacles. Their most remarkable feature is the complete absence of a gut. This has led to difficulties with classification because it is impossible to distinguish the ventral and dorsal surfaces. The animals are believed to obtain nourishment through a chemosymbiotic association (see CHEMOSYMBIOSIS) with bacteria. There are two groups, one found near vents and cold seeps, the other occurring widely in all oceans.

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Pogonophora

Pogonophora (beard worms) A phylum comprising deep-sea worms, first encountered in early Cambrian rocks but discovered only in this century. Beard worms are coelomate, with a superficial resemblance to Polychaeta, and live at great depths inside chitinous tubes they secrete for themselves in soft substrates. The body is divided into three parts. The anterior is crowned with tentacles. Part of the body is segmented and the worms have chaetae. Their most remarkable feature is the complete absence of a gut. This has led to difficulties with classification because it is impossible to distinguish the ventral and dorsal surfaces, and has also led to several theories concerning the method of feeding. The animals obtain nourishment by absorbing nutrients released by symbiotic bacteria. It has recently been proposed that the Pogonophora are actually very highly specialized Polychaeta.

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beardworms

beardworms See POGONOPHORA.

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Beardworms

Beardworms

Beardworms or pogonophorans, are slim, worm-like, marine invertabrates named for the thick cluster of long, fine, hairlike tentacles projecting from the front of the first section of their three-segmented bodies. 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 beardworms 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 reach 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 worms long narrow trunk are hundreds of tiny projectionsspecial glands that also secrete mucus, enabling it 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 tentaclesas many as 200,000 on a giant beardworm of the genus Riftia absorb all the nutrients the worm needs directly from the water. The females tentacles also serve a reproductive function. Although the species contains both sexes, beardworms do not mate because they never venture out of 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 females tube where egg fertilization takes place.

Living on the ocean floor at depths ranging from approximately 330 feet (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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Beardworms

Beardworms

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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