Pogonophora

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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.

Pogonophora

 

a phylum of marine invertebrates that live in long chitinous tubules that are open at both ends. The threadlike body ranges in length from a few centimeters to 1 m and consists of four sections. The first section is short and bears the prostomium and one to 2,000 tentacles. The second section has a frenulum consisting of a pair of cuticle keels that serve for support at the mouth of the tubule. The third segment is very long and bears the sex glands and attachment suckers and plates. The last section is used for digging and can protrude through the posterior opening of the tubule; it enables the animal to gradually burrow into the bottom of a body of water with its posterior end, while building onto its tubule not only from the front but also from the rear. Owing to this function, the body’s fourth section is divided by internal septa into a number of segments that bear short bristles.

Pogonophora have no intestine, mouth, or anus. They feed on organic substances that have dissolved in the water, absorbing them through their body surface and, especially, through their tentacles. There is a secondary body cavity (coelom), and the organs of excretion (coelomoducts) are in the first body section. The circulatory system includes a heart and the nervous system consists of a cephalic ganglion and an unpaired trunk. The sexes are separate. The embryo develops an entodermal intestine, which is later absorbed. The wall of the coelom is formed of lateral protrusions of the intestine.

Pogonophora are considered to be closely related to deutero-stomates, which acquired secondary segmentation in the posterior part of the body. Fossil tubules of Pogonophora are known from Lower Paleozoic marine deposits. Pogonophora are distributed in almost all seas at depths of 20 m and greater. There are more than 200 species, making up seven families.

REFERENCES

Ivanov, A. V. “Pogonofory.” In Fauna SSSR. Moscow-Leningrad, 1960.
Ivanov, A. V. “O stroenii zadnego otdela tela u Pogonophora.” Zoologi-cheskii zhurnal, 1964, vol. 43, issue 4, p. 581.
Livanov, N. A., and N. A. Porfir’eva. “Ob ‘annelidnoi gipoteze’ prois-khozhdeniia pogonofor.” Zoologicheskii zhurnal, 1965, vol. 44, issue 2, p. 161.

A. V. IVANOV

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.