من طرف Overview
News
Technology
Conditions of Use
Privacy Policy
Partners & Contributors
Awards & Recognition
ADW Staff
Contact Us
Spinning Skulls
About Mammals
Frog Calls
Resources for College Instructors
Resources for K-12 Instructors
Contribute to ADW
What's in a Scientific Name?
Authority Lists: Where We Get Our Names
Name, Rank, and Serial Number
Organismal classification: evolutionary relationships & ranks
Glossary
Search Guide
Related Links
Contact Us
Report an Error
Structured Inquiry Search — preview
Home Kingdom Animalia Phylum Nematoda
Phylum Nematoda
nematodes
Information Pictures Classification
2008/12/21 07:29:16.455 US/Eastern
By Phil Myers
Kingdom: Animalia
Phylum: Nematoda
Members of this Phylum
Roundworms (nematodes) are bilaterally symmetrical, worm-like organisms that are surrounded by a strong, flexible noncellular layer called a cuticle. Their body plan is simple. The cuticle is secreted by and covers a layer of epidermal cells. Near the body wall but under the epidermal cells are muscle cells; they run in the longitudinal direction only. A true coelom is lacking, instead, nematodes have a "pseudocoel" formed directly from the cavity of the blastula (rather than as a result of the division or folding of mesoderm). The cavity of the pseudocoel is small, being mostly filled with an intestine and oviducts or testes. A simple nervous system consists of a ring of nervous tissue around the pharynx that gives rise to dorsal and ventral nerve cords running the length of the body.
Nematodes move by contraction of the longitudinal muscles. Because their internal pressure is high, this causes the body to flex rather than flatten, and the animal moves by thrashing back and forth. No cilia or flagellae are present.
Some nematodes have specialized cells that excrete nitrogenous wastes; in others, canals or canals plus these specialized cells are present. Nematodes do not have flame cells.
Most nematodes are dioecious. Fertilization takes place when males use special copulatory spines to open the females' reproductive tracts and inject sperm into them. The sperm are unique in that they lack flagellae and move by pseudopodia, like amoebas. Development of fertilized eggs is usually direct.
Nematodes are almost unbelievably abundant. One study reported around 90,000 individual nematodes in a single rotting apple. Another reported 236 species living in a few cubic centimeters of mud. The number of described species is around 12,000, but too little attention has been paid to these animals and the true number may be closer to 500,000. Some species are generalists, occuring across wide areas and in many habitats; others are much more specialized. Nematodes have colonized nearly every conceivable habitat on earth, including such unlikely places as under beer coasters in Germany (Panagrellus redivivus). Some nematodes are also extreme habitat specialists, living, for example, only in the placentas of sperm whales (Placentonema gigantissima), or the right kidneys of minks (Dioctophyme renale)
Many nematodes are free living and play critical ecological roles as decomposers and predators on microorganisms. But nematodes also include parasitic species, a number of which affect humans directly or indirectly through their domestic animals. These include the common roundworms, which probably infest more than half the world's humans; hookworms; trichina, the worms that cause trichinosis; pinworms, another extremely common parasite, even in the United States, which can be transmitted from human to human by eggs floating in household dust; and filarial worms, primarily tropical parasites that cause diseases such as filariasis (elephantiasis) and onchocerciasis (river blindness).
--------------------------------------------------------------------------------
Source:
Hickman, C.P. and L. S. Roberts. 1994. Animal Diversity. Wm. C. Brown, Dubuque, IA.
Brusca, R. C., and G. J. Brusca. Invertebrates. 1990. Sinauer Associates, Sunderland, MA.
Chandler, A.C. 1961. Introduction to Parasitology. John Wiley and Sons, New York.
Lee, D.L. and H.J. Atkinson. 1976. Physiology of Nematodes (2nd ed.). Columbia University Press, New York.
Contributors
Phil Myers (author), Museum of Zoology, University of Michigan.
2008/12/21 07:29:16.825 US/Eastern
To cite this page: Myers, P. 2001. "Nematoda" (On-line), Animal Diversity Web. Accessed December 25, 2008 at [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]
Disclaimer: The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.
Other formats: OWL
Home ¦ About Us ¦ Special Topics ¦ Teaching ¦ About Animal Names ¦ Help
Structured Inquiry Search — preview
Sponsored in part by the Interagency Education Research Initiative,
the Homeland Foundation and the University of Michigan Museum of Zoology.
This material is based upon work supported by the National Science Foundation under Grants DUE-0633095 and DRL-0628151.
The ADW Team gratefully acknowledges their support. Report Error — Comment
1995-2008, The Regents of the University of Michigan and its licensors.
All rights reserved
News
Technology
Conditions of Use
Privacy Policy
Partners & Contributors
Awards & Recognition
ADW Staff
Contact Us
Spinning Skulls
About Mammals
Frog Calls
Resources for College Instructors
Resources for K-12 Instructors
Contribute to ADW
What's in a Scientific Name?
Authority Lists: Where We Get Our Names
Name, Rank, and Serial Number
Organismal classification: evolutionary relationships & ranks
Glossary
Search Guide
Related Links
Contact Us
Report an Error
Structured Inquiry Search — preview
Home Kingdom Animalia Phylum Nematoda
Phylum Nematoda
nematodes
Information Pictures Classification
2008/12/21 07:29:16.455 US/Eastern
By Phil Myers
Kingdom: Animalia
Phylum: Nematoda
Members of this Phylum
Roundworms (nematodes) are bilaterally symmetrical, worm-like organisms that are surrounded by a strong, flexible noncellular layer called a cuticle. Their body plan is simple. The cuticle is secreted by and covers a layer of epidermal cells. Near the body wall but under the epidermal cells are muscle cells; they run in the longitudinal direction only. A true coelom is lacking, instead, nematodes have a "pseudocoel" formed directly from the cavity of the blastula (rather than as a result of the division or folding of mesoderm). The cavity of the pseudocoel is small, being mostly filled with an intestine and oviducts or testes. A simple nervous system consists of a ring of nervous tissue around the pharynx that gives rise to dorsal and ventral nerve cords running the length of the body.
Nematodes move by contraction of the longitudinal muscles. Because their internal pressure is high, this causes the body to flex rather than flatten, and the animal moves by thrashing back and forth. No cilia or flagellae are present.
Some nematodes have specialized cells that excrete nitrogenous wastes; in others, canals or canals plus these specialized cells are present. Nematodes do not have flame cells.
Most nematodes are dioecious. Fertilization takes place when males use special copulatory spines to open the females' reproductive tracts and inject sperm into them. The sperm are unique in that they lack flagellae and move by pseudopodia, like amoebas. Development of fertilized eggs is usually direct.
Nematodes are almost unbelievably abundant. One study reported around 90,000 individual nematodes in a single rotting apple. Another reported 236 species living in a few cubic centimeters of mud. The number of described species is around 12,000, but too little attention has been paid to these animals and the true number may be closer to 500,000. Some species are generalists, occuring across wide areas and in many habitats; others are much more specialized. Nematodes have colonized nearly every conceivable habitat on earth, including such unlikely places as under beer coasters in Germany (Panagrellus redivivus). Some nematodes are also extreme habitat specialists, living, for example, only in the placentas of sperm whales (Placentonema gigantissima), or the right kidneys of minks (Dioctophyme renale)
Many nematodes are free living and play critical ecological roles as decomposers and predators on microorganisms. But nematodes also include parasitic species, a number of which affect humans directly or indirectly through their domestic animals. These include the common roundworms, which probably infest more than half the world's humans; hookworms; trichina, the worms that cause trichinosis; pinworms, another extremely common parasite, even in the United States, which can be transmitted from human to human by eggs floating in household dust; and filarial worms, primarily tropical parasites that cause diseases such as filariasis (elephantiasis) and onchocerciasis (river blindness).
--------------------------------------------------------------------------------
Source:
Hickman, C.P. and L. S. Roberts. 1994. Animal Diversity. Wm. C. Brown, Dubuque, IA.
Brusca, R. C., and G. J. Brusca. Invertebrates. 1990. Sinauer Associates, Sunderland, MA.
Chandler, A.C. 1961. Introduction to Parasitology. John Wiley and Sons, New York.
Lee, D.L. and H.J. Atkinson. 1976. Physiology of Nematodes (2nd ed.). Columbia University Press, New York.
Contributors
Phil Myers (author), Museum of Zoology, University of Michigan.
2008/12/21 07:29:16.825 US/Eastern
To cite this page: Myers, P. 2001. "Nematoda" (On-line), Animal Diversity Web. Accessed December 25, 2008 at [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]
Disclaimer: The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.
Other formats: OWL
Home ¦ About Us ¦ Special Topics ¦ Teaching ¦ About Animal Names ¦ Help
Structured Inquiry Search — preview
Sponsored in part by the Interagency Education Research Initiative,
the Homeland Foundation and the University of Michigan Museum of Zoology.
This material is based upon work supported by the National Science Foundation under Grants DUE-0633095 and DRL-0628151.
The ADW Team gratefully acknowledges their support. Report Error — Comment
1995-2008, The Regents of the University of Michigan and its licensors. All rights reserved
