Free Ebook of Invertebrates by Cambridge
 

[B]Free Ebook of Invertebrates By Janet Moore(An Introduction to Invertebrates)[/B]

[B]This is a link to ebook of invertebrate zoolgy.It cantains all the phylums.Hope its helpful.[/B]

[B][URL="http://www.scribd.com/doc/4961869/Invertebrates"]Click Here.[/URL][/B]

[B]Regards[/B]

Coelenterata
 

[B]Phylum Coelenterata Presentation with brief classification[/B]

[B][URL="http://www.scribd.com/doc/6710254/6-Cnidaria"]Check this[/URL][/B]


[B]Coral Reef Presentation with types.[/B]

[B][URL="http://www.scribd.com/doc/6710249/7-Corals-Coral-Reefs"]Click here[/URL][/B]

[B]Regards[/B]

coral reef
 

[B]Coral reefs[/B]
Coral reefs are warm, clear, shallow ocean habitats that are rich in life. The reef's massive structure is formed from coral polyps, tiny animals that live in colonies; when coral polyps die, they leave behind a hard, stony, branching structure made of limestone.

The coral provides shelter for many animals in this complex habitat, including [URL="http://www.enchantedlearning.com/subjects/invertebrates/sponge/"][COLOR=black]sponges[/COLOR][/URL][COLOR=black],[/COLOR] nudibranchs, fish (like Blacktip Reef Sharks, groupers, clown fish, eels, parrotfish, snapper, and scorpion fish), jellyfish, anemones, sea stars (including the destructive Crown of Thorns), crustaceans (like crabs, shrimp, and lobsters), turtles, sea snakes, snails, and mollusks (like octopuses, nautilus, and clams). Birds also feast on coral reef animals.
[B]Types of Corals[/B]: There are two types of coral, hard coral and soft coral. Hard corals (like brain coral and elkhorn coral) have hard, limestone skeletons which form the basis of coral reefs. Soft corals (like sea fingers and sea whips) do not build reefs.

[B]Where are Coral Reefs?[/B]: Coral reefs develop in shallow, warm water, usually near land, and mostly in the tropics; coral prefer temperatures between 70 and 85 ° F (21 - 30 °C). There are coral reefs off the eastern coast of Africa, off the southern coast of India, in the Red Sea, and off the coasts of northeast and northwest Australia and on to Polynesia. There are also coral reefs off the coast of Florida, USA, to the Caribbean, and down to Brazil.

The Great Barrier Reef (off the coast of NE Australia) is the largest coral reef in the world. It is over 1,257 miles (2000 km) long.

[B]Types of Reefs[/B]: The different types of reefs include:[LIST][*][B]Fringing reefs[/B] are reefs that form along a coastline. They grow on the continental shelf in shallow water.[*][B]Barrier reefs[/B] grow parallel to shorelines, but farther out, usually separated from the land by a deep lagoon. They are called barrier reefs because they form a barrier between the lagoon and the seas, impeding navigation.[*][B]Coral Atolls[/B] are rings of coral that grow on top of old, sunken volcanoes in the ocean. They begin as fringe reefs surrounding a volcanic island; then, as the volcano sinks, the reef continues to grow, and eventually only the reef remains.[/LIST][B]Coral Reefs in Danger[/B]: Many coral reefs are dying. Major threats to coral reefs are water pollution (from sewage and agricultural runoff), dredging off the coast, careless collecting of coral specimens, and sedimentation (when silt or sand from construction or mining projects muddies the waters of a reef and kills coral, which needs light to live).

[CENTER][IMG]http://www.geographyalltheway.com/igcse_geography/natural_environments/marine_processes/imagesetc/types_of_reefs.jpg[/IMG][/CENTER]

Nematocyst
 

[LEFT][FONT=Arial,Helvetica,sans-serif][SIZE=3][COLOR=#000000][B]What is a Nematocyst?[/B][/COLOR][/SIZE][/FONT][/LEFT]



[FONT=Arial,Helvetica,sans-serif][SIZE=3][COLOR=#000000]Nematocysts are unique to the phylum; Cnidaria ( = Coelenterata)[/COLOR][/SIZE][/FONT]


[FONT=Arial,Helvetica,sans-serif][SIZE=3][COLOR=#000000]Nematocysts are individual cells usually on the outer surface of the organism which have a variety of functions, most usually in defence or capture of prey species. These cells are known as stinging cells sometimes used to inject toxins which in some cases are toxic to man.[/COLOR][/SIZE][/FONT]


[FONT=Arial,Helvetica,sans-serif][SIZE=3][COLOR=#000000]Nematocysts can be specialised to carry out a number of functions within the organism these include; Sticking to surfaces and wrapping around objects, Penetrating surfaces or secreting proteinaceous toxins. These functions are used in food collection,defense and to some extent, locomotion. [/COLOR][/SIZE][/FONT]


[FONT=Arial,Helvetica,sans-serif][SIZE=3][COLOR=#000000]Nematocysts are usually most abundant on the feeding tentacles of all species, and within the digestive cavity of some species. The individual nematocyst rarely exceed 50 um (microns) in size, but is the great number that make them effective in providing protection or as a method to capture and stun prey species.[/COLOR][/SIZE][/FONT]
[FONT=Arial,Helvetica,sans-serif][SIZE=3][COLOR=#000000]These cells are also important to the biologist in individual species recognition.[/COLOR][/SIZE][/FONT]

[FONT=Arial,Helvetica,sans-serif][SIZE=3][COLOR=#000000]Nematocyst discharge is triggered by direct contact or other external stimulus. Once the cell is discharged a new nematocyst is formed as the mechanism in each cell can only be triggered once.[/COLOR][/SIZE][/FONT]

[CENTER][IMG]http://scyphozoans.tripod.com/sitebuildercontent/sitebuilderpictures/141997.jpg[/IMG][/CENTER]


[CENTER][IMG]http://biology.unm.edu/ccouncil/Biology_203/Images/SimpleAnimals/nematocysts%20diagram.gif[/IMG][/CENTER]

Phylum Platyhelmenthis
 

[LEFT][B][COLOR=black][FONT=Times New Roman]The Phylum Platyhelminthes[/FONT][/COLOR][/B][/LEFT]

[B][COLOR=black][FONT=Times New Roman][SIZE=3]Etymology:-[/SIZE][/FONT][/COLOR][/B][COLOR=black][SIZE=3][FONT=Times New Roman] From the Greek [I]platy[/I] for flat and [I]helminthes[/I] for worms,
Hence Flat Worms. [/FONT][/SIZE][/COLOR]
[COLOR=black]
[SIZE=3][FONT=Times New Roman][B]Characteristics of Platyhelminthes:-[/B]
1)Bilaterally symmetrical.
2)Body having 3 layers of tissues with organs and organelles.
3)Body contains no internal cavity.
4)Possesses a blind gut (i.e. it has a mouth but no anus)
5)Has Protonephridial excretory organs instead of an anus.
6)Has normally a nervous system of longitudinal fibres rather than a net.
7)Generally dorsoventrally flattened.
8)Reproduction mostly sexual as hermaphrodites.
9)Mostly they feed on animals and other smaller life forms.
10)Some species occur in all major habitats, including many as parasites of other animals. [/FONT][/SIZE][/COLOR]

[B][COLOR=black][FONT=Times New Roman]Platyhelminthes = Flatworms[/FONT][/COLOR][/B]

[COLOR=black][SIZE=3][FONT=Times New Roman]Platyhelminthes are an ancient phylum, but practically nothing is known of their evolutionary history because they have very soft bodies which do not preserve well as fossils. Scientists believe that the first turbellarians evolved around 550 MYA (million years ago).[/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]Platyhelminthes are mostly worm like creatures that are dorsoventrally flattened, meaning they look like a ribbon, this is why they are called names such as Tapeworm, Flatworm, Fluke and Planarian.[/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]The Platyhelminthes are a successful phylum with around 25,000 known species divided into four classes. Most Platyhelminthes are parasites on other animals, only the Turbellarians are mostly non-parasitic. A few species are commensalists living in harmony, or mutual benefit with another, normally larger organism. Most species feed on animal material either as parasites or as scavengers, a very few species feed on algae. Although a few of the free living marine and terrestrial species are very beautiful, most species are not particularly attractive to the human mind.[/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]Platyhelminthes live nearly everywhere, on land, in both fresh and marine waters as well as inside other animals. Most of the free living species are marine with only a small number inhabiting fresh water and very few being terrestrial. Parasitic species normally move between different habitats as they change life cycle stages and hosts. A number of parasitic species are of importance to mankind because they infect either our bodies or the bodies of our livestock. A few species can be fatal to humans if not treated, but nearly all species can be treated with modern medicines. Schistosomiasis (Bilharzia) is the most important platyhelminth disease of humans, causing much suffering and some death, over 200 million people are infected with the causative agent in tropical countries.[/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]While they remain fairly morphologically simple the Platyhelminthes show several advance in body structure over the simple radial phyla that came before them. They have a definite congregation of of sensory organs(a few have light sensing organs) and nervous tissues at one end of their body giving them a distinct head and tail. They also have distinct upper and lower (dorsal and ventral) body surfaces. They have a number of organs and even the beginnings of organ systems and a more distinct 3rd layer of cells in their body plan. The evolution of this connective tissue, called parenchyma, the cells of which serve as storage reservoirs as well as protecting the internal organs, is a major step forward toward the more complex body plans of higher animals, such as humans.[/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]However they still no anus, instead they have only a blind ending gut, or no gut at all. Those species with a gut must therefore excrete there digestive waste products through their mouths.[/FONT][/SIZE][/COLOR]
[B][COLOR=black][FONT=Times New Roman]Classification [/FONT][/COLOR][/B]

[FONT=Times New Roman][COLOR=black][SIZE=3]The higher classification of the Platyhelminthes, is as with so many other groups, in a state of confusion, and there is little consensus of opinion among the experts. The scheme I have used here will suffice to break the phylum into smaller, more manageable groups and will be satisfactory for teaching at secondary levels providing some mention is made of the inherent disharmony in expert opinion. However if you are considering research work, or writing as an undergraduate you should seek out and read the latest scientific papers. There is a general consensus concerning the classes Turbellaria and Cestoda, however the Monogenea, Digenea and the Aspidobothrians are somewhat confusing, you will find them all included in the Class Trematoda, and all given class status in their own right, and in schemes, like that which I have used here, that are a mixture of these two extremes.
[/SIZE][/COLOR][B][COLOR=black]Phylum Platyhelminthes[/COLOR][/B][/FONT][FONT=Times New Roman][COLOR=black][SIZE=3]
[/SIZE][/COLOR][B][COLOR=black]Class [URL="http://www.earthlife.net/inverts/turbellaria.html"][COLOR=black]Turbellaria[/COLOR][/URL][/COLOR][/B][/FONT][FONT=Times New Roman][COLOR=black][SIZE=3]
[/SIZE][/COLOR][B][COLOR=black]Class [URL="http://www.earthlife.net/inverts/monogenea.html"][COLOR=black]Monogenea[/COLOR][/URL][/COLOR][/B][/FONT][FONT=Times New Roman][COLOR=black][SIZE=3]
[/SIZE][/COLOR][B][COLOR=black]Class [URL="http://www.earthlife.net/inverts/trematoda.html"][COLOR=black]Trematoda[/COLOR][/URL][/COLOR][/B][/FONT][FONT=Times New Roman][COLOR=black][SIZE=3]
[/SIZE][/COLOR][B][COLOR=black]Class [URL="http://www.earthlife.net/inverts/cestoda.html"][COLOR=black]Cestoda[/COLOR][/URL][/COLOR][/B][/FONT]


[CENTER][FONT=Times New Roman][B][COLOR=black][IMG]http://teacherweb.com/NV/NWCTA/CarolTAdamson/Flatworms.gif[/IMG][/COLOR][/B][/FONT][/CENTER]

Phylum Platyhelminthes
 

[COLOR=black][FONT=Times New Roman][SIZE=4][B]Phylum Platyhelminthes[/B][/SIZE][/FONT][/COLOR]


[COLOR=black][FONT=Times New Roman][SIZE=4]This is a link to Power point Presentation [/SIZE][/FONT][/COLOR]


[COLOR=black][FONT=Times New Roman][SIZE=4][URL="http://faculty.evansville.edu/de3/b10802/PPoint/Platyhelminthes/sld001.htm"]Click here[/URL][/SIZE][/FONT][/COLOR]


[COLOR=black][FONT=Times New Roman][SIZE=4]This is a link to pdf file,all related to Flat worms.[/SIZE][/FONT][/COLOR]


[COLOR=black][FONT=Times New Roman][SIZE=4][URL="http://www.tamut.edu/~allard/Courses/Invertebrate_zoo/lectures/308_Lecture5.pdf"]Check this[/URL][/SIZE][/FONT][/COLOR]


[COLOR=black][FONT=Times New Roman][SIZE=4]regards[/SIZE][/FONT][/COLOR]

The life cycle of the liver fluke:
 

[COLOR=black][FONT=Times New Roman][SIZE=4][B][LEFT][FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=2][COLOR=#000080][COLOR=black][B]The life cycle of the liver fluke:[/B][/COLOR] [/COLOR][/SIZE][/FONT][/LEFT]
[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=2][COLOR=#000080]
[/COLOR][/SIZE][/FONT][/B][/SIZE][/FONT][/COLOR][LIST][*][LEFT]The adult flukes ([I]Fasciola hepatica[/I]: up to 30 mm by 13 mm; [I]F. gigantica[/I]: up to 75 mm) reside in the large biliary ducts of the mammalian host. Immature eggs are discharged in the biliary ducts and in the stool. [/LEFT][*][LEFT]After development in water, each egg releases a miracidium which invades a suitable snail intermediate host. [/LEFT][*][LEFT]In the snail the parasites undergo several developmental stages (sporocysts, rediae, and cercariae). [/LEFT][*][LEFT]The cercariae are released from the snail and encyst as metacercariae on aquatic vegetation or other surfaces. [/LEFT][*][LEFT]Mammals acquire the infection by eating vegetation containing metacercariae. [/LEFT][*][LEFT]After ingestion, the metacercariae excyst in the duodenum and migrate through the intestinal wall, the peritoneal cavity and the liver parenchyma into the biliary ducts, where they develop into adults.[/LEFT][*][LEFT][I]Fasciola hepatica[/I] infect various animal species, mostly herbivores. [/LEFT][*][LEFT]Humans can become infected by ingesting metacercariae-containing freshwater plants, especially watercress. [/LEFT][*][LEFT]In humans, maturation from metacercariae into adult flukes takes approximately 3 to 4 months.[/LEFT][/LIST][CENTER][IMG]http://uk.merial.com/producers/dairy/IMAGEFOLDER/life_cycle_of_liver_fluke.gif[/IMG][/CENTER]

Parasitic Adaptations in Helminths
 

[COLOR=black][FONT=Times New Roman][SIZE=4][B]Phylum Platyhelminthes[/B][/SIZE][/FONT][/COLOR]

[COLOR=black][B]Parasitic Adaptations in Helminths[/B][/COLOR]

Check this link for parasitic modification in flat worms,reproduction and life cycles.

[B][URL="http://www.scribd.com/doc/6710236/8-Parasitic-Adaptations-in-Helminths"]Click Here[/URL][/B]

regards

Importance of Trematodes
 

[B][FONT=Times New Roman][SIZE=4]Significance to humans[/SIZE][/FONT][/B]
[FONT=Arial][SIZE=3][FONT=Verdana]Trematodes pose a significant health threat to humans, particularly those living in developing countries. A common illness in developing countries is schistosomiasis. This condition, caused by three species of [I]Schistosoma[/I], affects more than 40 million individuals who live in tropical and subtropical countries, causing weakness, diarrhea, hemorrhage, fever, enlargement of the spleen, and other severe symptoms.[/FONT][/SIZE][/FONT]
[FONT=Arial][SIZE=3][FONT=Verdana]Other trematodes also infect humans, including the trematode [I]Opisthorchis[/I], which is transmitted to humans through eating infected fishes. Prevalent in parts of Russia, the fluke currently infects 1.2 million people, which is more than 4 percent of the region's population.[/FONT][/SIZE][/FONT]
[FONT=Arial][SIZE=3][FONT=Verdana]The cost for treatment of human fluke infections ranges into billions of dollars, in part because these conditions are frequently misdiagnosed. Treatment for infection by such organisms as [I]Paragonimus[/I] species costs about $1, but the patient's illness is often misinterpreted as tuberculosis, which calls for years of expensive treatment.[/FONT][/SIZE][/FONT]
[FONT=Arial][SIZE=3][FONT=Verdana]Trematodes that infect such household pets as rabbits, dogs, and cats may cause gastrointestinal symptoms requiring veterinary treatment. In the case of dogs, the trematode [I]Nanophyetus salmincola[/I] or so-called salmon-poisoning fluke, may cause a fatal disease resembling distemper because it carries a rickettsia (a type of bacterium) to which dogs are susceptible. The rickettsia, however, does not produce clinical disease in either humans or cats.[/FONT][/SIZE][/FONT]
[FONT=Arial][SIZE=3][FONT=Verdana]Trematodes can also infect livestock, sport and commercial fishes, and game mammals, which can have negative economic impacts on agriculture, sport fishing, and commercial fishing.[/FONT][/SIZE][/FONT][FONT=Arial]
[SIZE=3]Human infections are most common in the Orient, Africa, South America, or the Middle East. However, trematodes can be found anywhere that human waste is used as fertilizer.[/SIZE][/FONT]
[FONT=Arial][SIZE=3][FONT=Verdana]Trematodes are commonly referred to as [I]flukes[/I]. This term can be traced back to the Saxonname for Flounder, and refers to the flattened, rhomboidal shape of the worms. [/FONT][/SIZE][/FONT]
[FONT=Arial][SIZE=3][FONT=Verdana]There are no known cases of human infection with Aspidogastreans, therefore the use of the term "fluke" in relation to human infection refers solely to digenean infections. [/FONT][/SIZE][/FONT]
[FONT=Arial][SIZE=3][FONT=Verdana]The flukes can be classified into two groups, on the basis of the system which they infect. [B]Tissue flukes[/B], are species which infect the bile ducts, lungs, or other biological tissues. This group includes the lung fluke, [I]Paragonimus westermani[/I], and the liver flukes, [I]Clonorchis sinensis[/I] and [I]Fasciola hepatica[/I]. The other group are known as [B]blood flukes[/B], and inhabit the bloodin some stages of their life cycle. [/FONT][/SIZE][/FONT]

Phylum Aschelminthes
 

[B]Phylum Aschelminthes[/B]

[COLOR=black][FONT=Times New Roman][SIZE=3]A very large and heterogeneous cluster of [/SIZE][/FONT][URL="http://www.ucmp.berkeley.edu/phyla/phyla.html"][COLOR=black][FONT=Times New Roman][SIZE=3]animals[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman] have traditionally been classified together in a group variously known as the Aschelminthes, Nemathelminthes, and/or Pseudocoelomata. Today, these organisms are classified in about ten separate phyla. Nonetheless, it is sometimes useful to retain the name "Aschelminthes" to cover all these organisms. Opinion is divided as to whether or not the aschelminth phyla form one monophyletic group. To make matters worse, different authors have not agreed on what phyla should be considered "aschelminths." [/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]The most commonly recognized aschelminth phyla are: [/FONT][/SIZE][/COLOR][LIST][*][B][URL="http://www.ucmp.berkeley.edu/phyla/rotifera/rotifera.html"][COLOR=black][FONT=Times New Roman][SIZE=3]Acanthocephala[/SIZE][/FONT][/COLOR][/URL][/B][SIZE=3][FONT=Times New Roman] -- spiny-headed parasitic worms; about 1150 species known [/FONT][/SIZE][*][SIZE=3][FONT=Times New Roman][B]Chaetognatha[/B] -- arrowworms; about 70 species known. [/FONT][/SIZE][*][SIZE=3][FONT=Times New Roman][B]Cycliophora[/B] -- cycliophorans; 1 species known, microscopic [/FONT][/SIZE][*][SIZE=3][FONT=Times New Roman][B]Gastrotricha[/B] -- gastrotrichs; about 430 species known, all microscopic [/FONT][/SIZE][*][B][URL="http://www.ucmp.berkeley.edu/phyla/ecdysozoa/cephalorhyncha.html"][COLOR=black][FONT=Times New Roman][SIZE=3]Kinorhyncha[/SIZE][/FONT][/COLOR][/URL][/B][SIZE=3][FONT=Times New Roman] -- kinorhynchs; about 150 species known, all microscopic [/FONT][/SIZE][*][SIZE=3][FONT=Times New Roman][B]Loricifera[/B] -- loriciferans; about 10 species described, all microscopic [/FONT][/SIZE][*][B][URL="http://www.ucmp.berkeley.edu/phyla/ecdysozoa/nematoda.html"][COLOR=black][FONT=Times New Roman][SIZE=3]Nematoda[/SIZE][/FONT][/COLOR][/URL][/B][SIZE=3][FONT=Times New Roman] -- nematodes or roundworms; about 12,000 species known, but an estimated 200,000+ species extant, mostly microscopic [/FONT][/SIZE][*][SIZE=3][FONT=Times New Roman][B]Nematomorpha[/B] -- horsehair worms; about 320 species known [/FONT][/SIZE][*][B][URL="http://www.ucmp.berkeley.edu/phyla/ecdysozoa/cephalorhyncha.html"][COLOR=black][FONT=Times New Roman][SIZE=3]Priapulida[/SIZE][/FONT][/COLOR][/URL][/B][SIZE=3][FONT=Times New Roman] -- priapulid worms; 16 species known, abut half microscopic [/FONT][/SIZE][*][B][URL="http://www.ucmp.berkeley.edu/phyla/rotifera/rotifera.html"][COLOR=black][FONT=Times New Roman][SIZE=3]Rotifera[/SIZE][/FONT][/COLOR][/URL][/B][SIZE=3][FONT=Times New Roman] -- rotifers or "wheel animalcules"; about 1500 species known, all microscopic [/FONT][/SIZE][/LIST][COLOR=black][FONT=Times New Roman][SIZE=3]Of these, probably the most familiar is the Nematoda. Nematodes make up the second most diverse animal phylum, second only to the [/SIZE][/FONT][URL="http://www.ucmp.berkeley.edu/arthropoda/arthropoda.html"][COLOR=black][FONT=Times New Roman][SIZE=3]arthropods[/SIZE][/FONT][/COLOR][/URL][SIZE=3][FONT=Times New Roman]. Free-living nematodes are exteremely abundant in soils and sediments, where they feed on bacteria and detritus. Other nematodes are plant parasites and may cause disease in economically important crops. Still others parasitize animals (including humans); well-known parasitic nematodes include hookworms, pinworms, Guinea worm (genus [I]Dracunculus[/I]), and intestinal roundworms (genus [I]Ascaris[/I]). [/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]So what, if anything, is an aschelminth? Most are soft-bodied worms, and many of them are microscopic -- in fact, practically all members of the Cycliophora, Gastrotricha, Kinorhyncha, Loricifera, and Rotifera are less than 1 millimeter long, as are many nematodes and priapulids. On the other hand, one species of parasitic nematode can reach 13 meters in length -- it parasitizes the sperm whale -- and adult nematomorphs, chaetognaths, and some priapulids are also visible to the naked eye. [/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]Aschelminths used to be referred to as "[B]pseudocoelomates"[/B] -- an alternative name for the taxon is Pseudocoelomata -- because of their supposed shared internal structure. True [B]coelomates[/B] have a fluid-filled body cavity, the [B]coelom[/B], that surrounds the gut; this cavity exists within the middle tissue layer, the [B]mesoderm[/B], and the gut is suspended within it by sheets of tissue known as [B]mesenteries[/B]. "Pseudocoelomates" may also have a body cavity around the gut; in some (e.g. the gastrotrichs) it is extremely small, while in others (e.g. nematodes and priapulids) it may be quite extensive. This cavity has traditionally not been considered a true coelom, because it supposedly does not exist within the mesoderm, true mesenteries are not present, and its development in the embryo is quite different. However, this dichotomy between "coelomates" and "pseudocoelomates" appears to be false. A full discussion of this issue is beyond the scope of this exhibit; suffice it to say that some traditional "coelomates" and some traditional "pseudocoelomates" do not fit their traditional definitions. Body cavities develop in several different ways and perform many different functions within the animal kingdom. [/FONT][/SIZE][/COLOR]
[COLOR=black][SIZE=3][FONT=Times New Roman]A number of aschelminths [B]are parasitic[/B], including the Acanthocephala, which parasitize vertebrates; the Nematomorpha, which parasitize insects and other arthropods; and the Nematoda, which include parasites of plants and animals as well as many non-parasitic, free-living species. Free-living, microscopic "aschelminths" may be extremely common in moist soils and fresh-water sediments (gastrotrichs, rotifers and nematodes). Others may abound in marine sands and muds (gastrotrichs, kinorhynchs, loriciferans, nematodes, priapulids, rotifers). The arrowworms, found in marine waters, are generally planktonic and can swim; they are voracious predators on other planktonic organisms. Many small aschelminths, in particular many rotifers and nematodes, are able to suspend their life processes completely when conditions become unfavorable; in these resistant states they can survive extreme drying, heat, or cold, and then return to life when favorable conditions return. This is known as [B]cryptobiosis[/B]. [/FONT][/SIZE][/COLOR]
[COLOR=black][FONT=Times New Roman][SIZE=3]Since aschelminths all lack substantial hard parts, their fossil record is extremely spotty. Most of the microscopic phyla have no known fossil record at all, and seem unlikely ever to be found as recognizable fossils. The Rotifera are only known as far back as the [/SIZE][URL="http://www.ucmp.berkeley.edu/tertiary/oli.html"][SIZE=3][COLOR=black]Oligocene[/COLOR][/SIZE][/URL][SIZE=3]. Fossil nematodes are occasionally found in amber (fossilized tree resin) from the [/SIZE][URL="http://www.ucmp.berkeley.edu/cenozoic/cenozoic.html"][SIZE=3][COLOR=black]Cenozoic[/COLOR][/SIZE][/URL][SIZE=3], but possible fossil nematodes have been found in older rocks of the middle [/SIZE][URL="http://www.ucmp.berkeley.edu/paleozoic/paleozoic.html"][SIZE=3][COLOR=black]Paleozoic[/COLOR][/SIZE][/URL][SIZE=3]. The oldest known "aschelminth" phylum is the Priapulida. These unsegmented worms have been found in [/SIZE][URL="http://www.ucmp.berkeley.edu/cambrian/camb.html"][SIZE=3][COLOR=black]Cambrian[/COLOR][/SIZE][/URL][SIZE=3] rocks, such as the legendary Burgess Shale. Priapulids, at least, date from the earliest known evolutionary radiation of the animals, and a few trace fossils suggest that nematodes may have been around at the time as well. Evidence from the anatomy and genetic information of living "aschelminths" suggest that the aschelminth phyla are much older than their sparse fossils would indicate. However, no consensus has yet been reached as to how these phyla evolved and how they are related to each other.[/SIZE][/FONT][/COLOR]

[CENTER][COLOR=black][FONT=Times New Roman][IMG]http://content.tutorvista.com/biology_11/content/us/class11biology/chapter10/images/img69.jpeg[/IMG] [/FONT][/COLOR][/CENTER]
[COLOR=black][FONT=Times New Roman]Round Worm Anatomy[/FONT][/COLOR]