Proglottids can be filled with up to , eggs! The Tapeworm Life Cycle With few exceptions, all cestodes require at least two hosts, and the adult is the parasite in the digestive tract of vertebrates. Often one of the intermediate hosts is an invertebrate most often an arthropod such as a flea, louse or copepod that is eaten by the final host.
The eggs within the proglottids are shed daily in the feces into the soil where they may lie dormant for quite some time. Sometimes the egg-bearing proglottids crawl out of the anus by themselves and can be found wriggling about on an infected dog, cat or child or on infected clothing and bedding.
Once the eggs are released, they must be ingested by an intermediate host in order to hatch into hooked larvae called oncospheres, which bore through the intestinal wall and picked up by the circulatory system where they are transported to skeletal muscle, heart or even some other organ where they encyst as cysticerci bladder worms.
Tapeworm Infection in Humans Humans can become infected with tapeworms by eating poorly cooked meat containing the cysticerci of the tapeworm. The most important tapeworms that infect humans are the beef tapeworm Taenia saginata and the pork tapeworm Taenia solium. Another species of cestode that can infect humans is the broad fish tapeworm Diphyllobothrium latum , which is common in fish inhabiting the Great Lakes. Again, infection occurs by ingesting cysticerci in raw or poorly cooked fish. In most cases, tapeworms found in the gut do not cause much damage to their human hosts, but occasionally they migrate to other organs such as the eyes or even the brain, where they can cause serious neurological problems and even death from cerebral cysticercosis!
The dog tapeworm Diplydium caninum is common in dogs but can be picked up by humans usually kids who ingest infected fleas that serve as intermediate hosts of the parasite.
In contrast to radiate and acoelomate phyla in which the space between the body wall and the digestive tract is filled with mesoglea or with solid mesenchymal parenchyma, the remaining bilateral animals covered in the Zoo Lab website have a body cavity in which internal organs are located.
In the pseudocoelomates, the embryonic blastocoel persists as a body cavity. The Phylum Acanthocephala contains about 1, species of parasitic animals called spiny-headed worms, all of which are endoparasites in the intestinal tracts of vertebrates especially fishes. Two hosts are required to complete the life cycle, and the juveniles are parasites of crustaceans and insects. Most species are quite small less than 40 mm. Spiny-headed worms have an eversible proboscis covered with recurved spines that provides a means of attachment in the host's intestine.
Eggs pass out host and are eaten by certain insects or crustaceans where they hatch and go through several developmental stages. When the intermediate host is eaten by a bird, mammal or fish, the larva inside attaches to the intestinal wall with its spiny proboscis. The Phylum Rotifera contains about 1, species of microscopic animals called rotifers that bear an anterior crown of cilia that give the appearance of a revolving wheel.
Although cosmopolitan widely distributed , most are found only in freshwater environments. The general body plan of a rotifer is divided into three regions: a head, which bears a ciliated organ called a corona wheel organ , which creates currents that draw small planktonic forms into the mouth, which opens into a muscular pharynx called a mastax. The mastax is equipped with intricate jaws composed of seven hard pieces called trophi that are used for grasping and chewing the prey.
The trunk contains the visceral organs, and the foot when present is segmented and ringed into joints that can shorten or telescope. Pedal glands on the foot secrete a sticky substance that anchors the animal to the substrate or allows it to creep along with leech like movements. From this point on, all animals that will be studied in the Zoo Lab website are eucoelomate, that is, they have a true coelom body cavity that is lined with a thin layer of mesodermal tissue called the peritoneum.
Note: The development of the coelom must be considered one of the most important steps in the evolution of larger and more complex forms for it provides plenty of space for organs that can be held in place by thin membranes called mesenteries! The Phylum Ectoprocta also called Bryozoa contains about 4, species of small colonial forms called moss animals that are found in shallow freshwater and marine environments. Although bryozoans are also well represented in the fossil record, they are also quite abundant today.
Modern marine forms exploit all kinds of firm substrates including shells, rocks, marine timbers, and ship bottoms.
In fact, like barnacles, the ectoprocts are one of the most important groups of fouling organisms that need to be removed periodically from ship and boat hulls. Each individual zooid consists of a feeding part and a case-forming part.
The zoecium can be gelatinous, chitinous or calcareous, and sometimes it is impregnated with sand grains. The feeding portion of the animal contains the lophophore a ciliated feeding device that can also be used for gas exchange , digestive tract, muscles and nervous system. This is an ancient group that is well represented in the fossil record with some 30, described species but only about living species.
Brachiopods resemble bivalve molluscs, but unlike bivalves, they have shells that are located on the ventral and dorsal side rather than left and right.
Brachiopods in the latter group are called lampshells because the larger ventral valve resembles a Roman oil lamp. Some brachiopods attach themselves to the substrate by a pedicel on the ventral valve while others just cement the ventral valve to the substrate like an oyster or burrow into the sediment.
Like bryozoans, brachiopods also have a lophophore surrounding the mouth that is used for feeding and gas exchange. Lab-5 This slide contains two specimens of the free-living turbellarian flatworm Planaria. One specimen has been stained, while the other has been injected with carbon black to reveal the extent of the blind gastrovascular cavity, which is divided into three, many-branched trunks one anterior and two posterior.
Without an anus, food must first pass through the mouth into the gastrovascular cavity where it is digested after which waste products exit through the same opening. Note the large, eversible pharynx in each planarian that is used for feeding. In the head region are lateral projections called auricles not well developed on the specimens shown that contain touch and chemical receptors as well as light-sensitive ocelli eye spots.
This slide contains a cross section through the pharyngeal middle region of the free-living flatworm Planaria. Note the large muscular pharynx that lies within a space called the buccal cavity. During feeding, the pharynx can be everted through the mouth and used to suck up fluids and soft tissue from captured prey. Two branches of the extensive gastrovascular cavity can also be seen.
This cavity is lined with large, vacuolated cells that comprise the gastrodermis. On the outside of the flatworm is a ciliated epidermis that contains many gland cells as well as dark-staining rod-shaped bodies called rhabdites that can discharge their contents to form a protective mucous layer around the body. Lacking a body cavity, the space between the gut and epidermis in these acoelomates is filled with a meshwork of mesodermal parenchyma as well as muscle fibers that run circularly, longitudinally and diagonally.
This slide shows a stained whole mount of the Oriental liver fluke Clonorchis sinensis , an important trematode parasite of the humans in many regions of Asia, especially China, Southeast Asia and Japan.
Humans are infected by eating raw or poorly cooked fish containing the encysted metacercariae. After being ingested, these cysts dissolve in the intestine, releasing the young flukes which then migrate to the bile duct and liver.
This slide shows the redia larva of a trematode parasite. This larval stage normally develops in the tissues of an aquatic snail. The redia contains groups of cells called "germ balls" that eventually develop into the tailed cercaria larvae, which emerge from the snail and penetrate a second intermediate host or encyst on vegetation to become a metacercaria.
This slide shows the tailed-cercaria larva of a trematode parasite. This larval stage, which normally develops in the tissue of an aquatic snail, will emerge from its intermediate host and penetrate a second intermediate host or encyst on vegetation to become a metacercaria.
This slide contains stained sections of the dog tapeworm Diplydium caninum taken from four different regions. The rest of the body is divided into a linear series of segments called proglottids, each of which contains a complete set of reproductive organs. The youngest proglottids in the first part of the strobila body of the tapeworm are immature, while those in the middle are mature. The oldest terminal proglottids are gravid, which means they are filled with eggs. Dogs and cats can become infected by eating adult fleas the intermediate hosts containing cysticercoid larvae.
This slide shows a mature proglottid from the dog tapeworm Diplydium caninum. Note that there are two complete sets of male and female reproductive structures that include testes, vasa deferentia the plural of vas deferens , ovaries, yolk glands, vaginas and genital pores. Dogs and cats become infected by eating adult fleas the intermediate hosts containing cysticercoid larvae.
This slide shows a mature proglottid from the tapeworm Taenia pisiformis, a species commonly found in the small intestines of dogs and cats. Note that each segment contains a complete set of reproductive structures including testes, vas deferens sperm duct , ovary, yolk gland, vagina and genital pore. This slide shows a scolex from the anterior most region of the tapeworm Taenia pisiformis. Note the series of hooks on a raised portion of the scolex called a rostellum as well as the four lateral suckers.
These hooks and suckers enable to tapeworm to remain attached to the intestinal wall of its host. This slide shows a magnified view of the raised tip of the scolex rostellum from the dog and cat tapeworm Taenia pisiformis.
Note the formidable array of hooks that are used by the tapeworm to hang on to the intestinal tract of its host. This slide shows the cysticercus larva of the tapeworm Taenia pisiformis. Note the invaginated scolex on the right end of this "bladder worm". After infected tissue of the intermediate host is eaten by the definitive host, the scolex everts and attaches to the lining of the intestine by means of hooks and suckers. This slide shows a stained specimen of an adult spiny-headed worm belonging to the Phylum Acanthocephala.
Although human infections have been recorded, adult worms normally parasitize the digestive tracts of fish, birds and domestic and wild mammals. The larvae of spiny-headed worms develop in various species of crustaceans or insects. Note the everted proboscis containing numerous recurved spines that give the organism its name. These spines which permit the worms to remain attached to the digestive tract can cause massive and sometimes painful destruction of the intestinal mucosa.
This slides shows two stained rotifers. These pseudocoelomate animals derive their name from a distinctive ciliated crown corona that, when beating, gives the impression of a rotating wheel. The movement of these cilia creates water currents that draw food items into the mouth of the organism. Once inside, food is chewed and ground up in a muscular portion of the pharynx called a mastax that is equipped with small hard jaws called trophi. Although there are a few marine species, most rotifers are found in freshwater habitats throughout the world.
This microscope image shows two live specimens of the common rotifer Philodina. Note the lateral extension of the body wall in the head region of the specimen on the right pointed to by the red arrow. This structure which is called an antenna contains many, tiny sensory bristles. The corona "wheel organ" containing two large ciliated trochal discs and foot with its two toes the spurs pointed to by the blue arrow can be seen on the specimen on the left.
Pedal glands which open by ducts at the tips of the toes produce an adhesive substance used for temporary attachment to the substrate. This microscope image shows a magnified view of the freshwater rotifer Philodina.
Note the conspicuous corona wheel organ with its cilia and the centrally-located mastax pointed to by the red arrow , a muscular portion of the pharynx equipped with chitinous jaws trophi that grind and shred ingested food. This microscope image shows another species of rotifer in the genus Monostyla.
This common freshwater species has a rigid, chitin-like covering called a lorica. This slide shows several zooids of the freshwater ectoproct Plumatella. Note the conspicuous lophophores. These feeding devices consist of masses of ciliated tentacles borne on ridges surrounding the mouth. In addition to reproducing by budding, freshwater bryozoans reproduce asexually by means of special resistant bodies called statoblasts not visible on this slide.
These dark, disc-shaped structures which are similar to the gemmules of freshwater sponges are produced during the summer and fall, and can remain dormant until environmental conditions improve in the spring. This slide shows a portion of a branching colony of the marine bryozoan ectoproct Bugula. Branching within the colony is produced by repeated asexual budding of individuals called zooids.
Note the tentacles of the lophophores ciliated feeding devices surrounding the mouth that can also be used for gas exchange. Like many colonial cnidarians, ectoproct colonies are polymorphic, with most of the zooids functioning as feeding individuals. Defensive zooids called avicularia protect the colony against small organisms, including settling larvae and crawling tube-building polychaete worms and arthropods.
Each avicularium resembles the head of a bird complete with powerful musculature and a sharp beak-like structure rostrum that is used to seize the appendages of trespassing organisms. This slide shows a magnified view of an avicularium from the marine colonial bryozoan Bugula. Note the mandible, bird-like beak which is called a rostrum and musculature. Avicularia protect the colony from small organisms, including settling larvae and crawling tube-building polychaete worms and arthropods.
This is a slide of a monogenetic fluke taken from the gills of an Atlantic stingray. Unlike the digenetic trematodes, monogenetic species have a direct life cycle in which ciliated larvae called oncomiracidia develop on or within a single host.
Although a few species are found in the urinary bladders of frogs and turtles, most such flukes cling to the gills and external surfaces of fish by means of a posterior attachment organ called an opisthaptor that is equipped with hooks. This slide shows a stained whole mount of the sheep liver fluke Fasciola hepatica. This large trematode is a common parasite of sheep and cattle, which become infected by eating aquatic plants containing the encysted metacercariae juvenile flukes.
Once ingested, the cyst walls are digested and the larvae burrow through the intestinal wall to the body cavity and eventually to the liver. This slide shows an adult specimen of the lung fluke Paragonimus westermani.
Found in east Asia, southwest Pacific and some parts of South America, the fluke parasitizes a number of wild carnivores, pigs, rodents and humans.
Infection with lung flukes causes respiratory symptoms, with breathing difficulties and chronic cough, and fatalities are common!
Humans get infected with lung flukes by eating raw or poorly-cooked freshwater crabs containing the fluke metacercariae. This slide shows a pair of adult blood flukes in copulation. Blood flukes differ from most other flukes by being dioecious i. Males are larger and have a large, ventral groove called a gynecophoric canal posterior to the ventral sucker that holds the smaller more darkly stained female during copulation, which is continuous. Schistosoma mansoni is one of the three species of blood flukes responsible for the disease in humans called schistosomiasis.
Humans get infected when the tailed cercaria larvae which escape from freshwater snails that serve as their intermediate hosts burrow into the exposed skin of individuals bathing, swimming or working in such habitats. This model includes several views of a free-living turbellarian flatworm. The image on the left shows the nervous system painted white , which consists of a pair of cerebral ganglia with two ventral nerve cords that are connected by a series of transverse nerves called commissures, giving it a ladder-like appearance.
Other sensory structures include simple, light-sensitive eyes ocelli and chemical receptors that are concentrated in lateral projections of the head called auricles because they look like ear lobes. Although reproduction in planarians can occur asexually through fission, all forms are monoecious with both male and female reproductive organs.
Several features of the reproductive system shown in blue and yellow are also seen on the model on the left. The model on the right shows the many branched gastrovascular cavity shown in red that exits through a single ventral opening at the end of a muscular, eversible pharynx shown in off-white on both models as well as on the small upper planarian model. Protonephridia consist of excretory tubules that are closed internally and open to the outside by a series of collecting ducts that lead to a posterior opening called a nephridiopore.
The internal ends of each of these tubules terminate in so-called flame cells one of which is shown on the small, lower model , which have tufts of cilia that flicker like the flame of a candle.
The beating of these cilia pulls water through a mesh-like cup, producing a filtrate of water and small molecules. This image shows a model of the Oriental liver fluke Clonorchis sinensis , an important trematode parasite of the humans in many regions of Asia. Humans are infected by eating raw or under cooked fish containing the encysted metacercariae. For close-up views of labeled structures found in different sections of the liver fluke, click on the links below.
Mouth; 2. Oral sucker; 3. Esophagus; 4. Intestinal ceca; 5. Ventral sucker; 6. Genital pore; 7. Uterus; 8. Two ventral nerve cords extend from the brain to the posterior of the planarian.
The two ventral nerve cords are connected to one another by smaller nerves. Additionally, the planarian has two visible sensory organs. The auricles are lateral flaps near the anterior of the animal. The auricles are chemoreceptors and sense chemicals in the water. Also near the anterior are two eyespots. These allow the flatworm to sense whether it is darkness or light.
It does not allow to animal to see images. Once a planarian has sensed food, moved to it, and ingested it, the food is digested by both extracellular digestion and intracellular digestion. The lining of the gastrovascular cavity the gastrodermis releases digestive enzymes into the GVC.
The ingested food is broken down to small food particles by this process. The small food particles are then taken into the gastrodermis cells by endocytosis. Within food vacuoles formed by endocytosis, the food particles are further broken down to food molecules.
These food molecules diffuse or are actively transported into the cytoplasm of the gastrodermis cell. Food is distributed from the gastrodermis to other cells of the body by diffusion primarily. Since flatworms are small distribution of food by diffusion is possible. Food digestion produces digestive waste. This is released from the planarian through the mouth. The digestion of proteins produces nitrogen waste ammonia.
The planarian has a system of tubules extending throughout its body from the anterior to posterior on both sided of the body. These tubules are called protonephridia and they collect both excess water and much of the nitrogen waste. The tubules have pores that lead out of the body. Water and ammonia leaves through these pores. Aerobic respiration produces carbon dioxide as a waste product.
This is released from the planarian by diffusion. To carry out aerobic respiration, the planarian must get oxygen to the cells of its body. Oxygen enters the planarian by diffusion. The special features of the Phylum Platyhelminthes includes the protonephridia.
These structures can be considered primitive kidneys. They are unique to the phylum. Planarians are placed in the Class Turbellaria, and these were discussed extensively above. The flukes Class Trematoda are mostly parasites of vertebrate animals those with backbones. The animals generally have a sucker around the mouth and one on the ventral surface.
These suckers allow the animal to cling to the body organs in which they live. The adult flukes live in hollow organs like the heart, tongue, kidney, and gall bladder on lower surface of the liver.
Many flukes have immature stages that live in other animals. For example, immature stages larvae of the human liver fluke live in snails.
These are released from snails, and a second immature stage then lives within fish. When humans ingest raw or undercooked fish, they also ingest immature stages of the fluke. The immature stages migrate to the bile ducts of the liver where they mature. The mature stages may live within the bile ducts for years. While there they cause damage of the liver and may cause death of the human host.
Eggs are produced by the adult within the bile ducts. The eggs travel through the bile ducts to the digestive tract and pass out of the host in feces. The eggs are ingested by snails, and the cycle is repeated.
Humans can also become infected with a human blood fluke. Immature stages of this fluke also live within snails. These larvae leave the snail and are present on the ground in areas of poor sanitation. The immature stages enter humans by burrowing through the skin of a human host. The immature flukes enter blood vessels and mature there. They can cause anemia and damage to the liver, bladder, and brain. Tapeworms Class Cestoda are also parasite flatworms.
Humans can become infected with tapeworms by ingesting uncooked or undercooked pork or beef. Larval immature stages of the tapeworm present in the muscle of pigs or cows are ingested. The tapeworm attaches to the intestine while passing through the digestive tract using hooks or suckers. The tapeworm matures and grows in the intestine, a food-rich environment. The tapeworm grows longer by budding. Each proglottid contains reproductive structures and eggs are produced and become fertilized within each segment.
The oldest proglottids break off of the tapeworm and leave the host with feces. In areas of poor sanitation, pigs or cows ingest the zygotes. The immature stages burrow into the muscle tissue of the pig or cow and the cycle repeats. The impact the Phylum Platyhelminthes has on humans is the fact that several animals within the phylum are human parasites. The Phylum Nematoda roundworms or nematodes includes harmless, soil-dwelling roundworms nematodes that eat decaying organic material or small soil animals.
The phylum also includes plant parasites that infect the roots of plants. These parasitic nematodes decrease the productivity of many human crops.
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