Pogonophora

Pogonophora [‚pō·gə′näf·ə·rə]

(invertebrate zoology)

The single class of the phylum Brachiata; the elongate body consists of three segments, each with a separate coelom; there is no mouth, anus, or digestive canal, and sexes are separate.

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Pogonophora

The beard worms—a phylum of sedentary marine worms living in cool waters of all the world's oceans, generally at depths between 330 and 13,200 ft (100 and 4000 m), shallower at higher latitudes and deeper in trenches. They were first dredged late in the nineteenth century but first investigated in the 1950s. Pogonophorans construct a tube, and are the only nonparasitic metazoans to have no mouth, gut, or anus in their postembryonic anatomy. These are long, slender worms, the diameter in most being less than 1 mm and the length being over 100 times the diameter. Superficially the tubes remind one of corn silk or coarse thread, but most have a characteristic banding pattern with annuli of brown or yellow pigments. The larger tubes are sometimes rigid, thicker, and darkcolored.

The evidence now suggests that these worms absorb their nutrients, such as amino acids, glucose, and fatty acids, through the pinnules and microvilli of the tentacles without the aid of digestive enzymes. This is accomplished against concentration gradients and may be supplemented by limited pinocytosis and phagocytosis by tentacular surfaces in a few species. The presence of internal symbiotic bacteria was demonstrated in several genera. These chemosynthetic organisms also play an important role in providing nutrients to these worms.

The sexes are separate, with the gonopore location being the only sexual dimorphism. Spermatophores with long tail filaments are released by the male. Fertilization has not been observed but must occur within the maternal tube, as fertilized eggs and developing larvae have been found there.

The Pogonophora consist of two orders: Athecanephria and Thecanephria.