Relationship to Humans:
Tapeworms are parasites that reside in the digestive track of vertebrates, such as humans. They often gain entry when people consume raw or under cooked meats and then live in the intestines, where they feed of off human wastes. (2). Luckily, taking an "anti-worm medication" will wipe out tape worms inside a host's body in the first dosage (3).
Tapeworms can also cause neurocysticercosis, which is a diseased caused by tapeworm cysts in the human brain. When the tapeworm eggs are ingested by another human rather than a pig, the larvae burrow into the bloodstream, sprouting grape-like extentions to cloak itself from the immune system and may thrive there for years. They may arrive at the brain and form cysts there, or clog a passageway (10). (9)
Some people consume tapeworms to lose weight (3).
Habitat and Niche:
Tape worms inhabit intermediate and final hosts. Larval tape worms live in cysts in the body tissues of intermediate hosts. When the intermediate host is consumed by the final host, the tape worm remains in the final host's intestine and matures there. Adult tape worms absorb nutrients from the final host as they pass through the intestine. (5)
Predator Avoidance:
While tapeworms do not really have any predators, they must avoid the host's immune response if they are to live inside a host. Tapeworms can periodically modify surface glycoproteins to evade detection by the host's immune system. The glycoproteins on the surface of tapeworm cells are essentially antigens, so by constantly modifying these proteins, immune cells have a harder time binding to tapeworm cells and initiating an immune response (10).
Nutrient Acquisition:
Tapeworms hook on to the intestines and absorbs nutrients that have already been broken down by the host's digestive system. Tapeworms do not have digestive systems of their own (3).
Cestodes lack any trace of a digestive tract and therefore must absorb all required substances through their external covering. Before 1960, the body covering of cestodes and trematodes was commonly referred to as a "cuticle", but it is now known that it is a living tissue with high metabolic activity and is synonymous to the term "tegument". Tegumental structure is generally similar in all cestodes studied, differing in details according to species. The tegument is covered by minute projections called microtriches that are underlaid by the tegumental distal cytoplasm. The distal cytoplasm is connected to perikarya by trabeculae that run through superficial muscle layer. The microtriches are similar in some respects to the microvilli found on gut mucosal cells and other vertebrate and invertebrate transport epithelia, and they completely cover the worm's surface, including the suckers. The cytoplasm of the base is continuous with that of the rest of the tegument, and the entire structure is covered by a plasma membrane. A layer of carbohydrate-containing macromolecules, the glycocalyx, is found on the membrane. The microtriches serve to increase the absorptive area of the tegument, but they also may help the worm maintain its position in the host gut. (7, 340/357)
Reproduction and Life cycle:
Segments called "proglottids [are] either male or female", and the tape worm can produce "millions of fertilized eggs" (3). Most tapeworms are hermaphroditic, meaning that an individual contains functional reproductive organs of both sexes. They are usually self-fertilizing. (8)
Sexually mature tapeworms live in the intestine or its diverticulae. A mature tapeworm may live for a few days or up to many years, depending on the species. During its reproductive life, a single worm produces from a few to millions of eggs, each with the potential of developing into the adult form. Because of the great hazards obstructing the course of transmission and development of each worm, mortality is very high. Most tapeworms are hermaphroditic and are capable of fertilizing their own eggs. Sperm transfer is usually from the cirrus to the vagina of the same segment or between adjacent strobilae, if the opportunity permits. A few species of tapeworms are known in which a vagina is absent; hypodermic impregnation has been observed in some of these. In such cases, the cirrus is forced through the body wall, and the sperm are deposited within the parenchyma. How they find their way into the seminal receptacle is unknown. (7,348)
Growth and development:
There are multiple steps in the developmental process of the juvenile forms of tapeworms: 1) Embryogenesis- within the egg to result in a larva, the oncosphere 2) Hatching of the oncosphere after or before being eaten by the next host, where it penetrates to a parenteral site 3) Metamorphosis of the larva in the parenteral site into a juvenile, or metacestode, usually with a scolex 4) The development of the adult from the metacestode in the intestine of the same or another host. The oncospheres of all Eucestoda have thee pairs of hooks, and are thus also referred to as hexacanths. The free-swimming oncospheres hatching from the egg of some pseudophyllideans and a few trypanorhynchans have a ciliated embryophore and are called coracidia. The larvae of cestodarians have ten hooks and are called decacanths, which are also ciliated and are called lycophoras. (7, 353)
Integument:
The outer layer of the tape worm consists of an epidermis. This layer is made up of a ciliated, cellular epithelium possessing glands and sensory nerve endings. The glands secrete numerous substances, some of which can help trap prey. A basement membrane, or duplicate membrane that separates the epithelium from underlying tissue, provides structure for the organism (6). The tapeworm's outer layer is tough and protective, providing defense from the host's digestive juices (11).
Movement:
Movement of tapeworms is aided by the adhesive and releaser glands.
(12)
Commonly, between the scolex and the strobila lies an undifferentiated zone called the neck, which may be long or short. It contains germinal cells that are responsible for giving rise to new proglottids. Longitudinal muscles are arranged around a central mesenchymal area, largely free of longitudinal fibers. The pattern and development of muscle bundles promote extraordinary mobility. (7, 342)
Sensing the Environment: The scolex contains the chief neural ganglia of the worm, and it bears numerous sensory endings on its anterior surface, likely detecting both physical and chemical stimuli. Such sensory input may allow optimal placement of the scolex and entire strobila with respect to the gut surface and physicochemical gradients within the intestinal milieu. The main nerve center of the cestode is in its scolex, and the complexity of ganglia, commissures, and motor and sensory innervation there depends on the number and complexity of other structures on the scolex. Arising from the cerebral ganglia are a pair of anterior nerves, supplying the apical region of the scolex; four short posterior nerves; and a pair of lateral nerves that continue posteriorly through the strobila. The bothria are innervated by small branches to form the lateral nerves. In addition to the motor innervation of the scolex, there may be sensory endings, particularly at the apex of the tegument. (7, 338/342) Tapeworms have simple eye spots that allow them to distinguish dark from light, and they are aversive to sources of intense light (11).
Gas Exchange: Tapeworms do not have respiratory systems to control gas exchange. Instead, gas is diffused directly across the membranes of their cells. This is possible, for their flat body results in a high surface area to volume ratio (13).
Waste Removal: In cestodes, the main osmoregulatory canals run the length of the strobila from the scolex to the posterior end. These are usually in two pairs, one ventrolateral and the other dorsolateral on each side. The canals may branch and rejoin throghout the strobila or may be independent. Usually a transverse canal joins the ventral canals at the posterior margin of each proglottid. The dorsal and ventral canals unite in the scolex, often with some degree of branching. Posteriorly, the two pairs of canals merge into an excretory bladder with a single pore to the outside. Rarely, the major canals also empty through short, lateral ducts. Although this system is often called the "osmoregulatory", it is also commonly referred to as the "excretory system". (7, 344)
Environmental physiology (temperature, water and salt regulation)
Internal Circulation:
Tapeworms lack a circulatory system. (8)
Chemical Control:
Review Questions:
1. Explain what it means when someone says Tapeworms are hermaphroditic. 2. How do proglottids play into reproduction?
3. How do tapeworms infect two hosts and how do they travel from one to another?
Classification/ Diagnostic characteristics:
Kingdom: Animalia
Class: CestodaPhylum: Platyhelminthes
Order: Cyclophyllidea
Family: Taeniidae
Genus: Taenia (4)
Relationship to Humans:
Tapeworms are parasites that reside in the digestive track of vertebrates, such as humans. They often gain entry when people consume raw or under cooked meats and then live in the intestines, where they feed of off human wastes. (2). Luckily, taking an "anti-worm medication" will wipe out tape worms inside a host's body in the first dosage (3).
Tapeworms can also cause neurocysticercosis, which is a diseased caused by tapeworm cysts in the human brain. When the tapeworm eggs are ingested by another human rather than a pig, the larvae burrow into the bloodstream, sprouting grape-like extentions to cloak itself from the immune system and may thrive there for years. They may arrive at the brain and form cysts there, or clog a passageway (10).
(9)
Some people consume tapeworms to lose weight (3).
Habitat and Niche:
Tape worms inhabit intermediate and final hosts. Larval tape worms live in cysts in the body tissues of intermediate hosts. When the intermediate host is consumed by the final host, the tape worm remains in the final host's intestine and matures there. Adult tape worms absorb nutrients from the final host as they pass through the intestine. (5)
Predator Avoidance:
While tapeworms do not really have any predators, they must avoid the host's immune response if they are to live inside a host. Tapeworms can periodically modify surface glycoproteins to evade detection by the host's immune system. The glycoproteins on the surface of tapeworm cells are essentially antigens, so by constantly modifying these proteins, immune cells have a harder time binding to tapeworm cells and initiating an immune response (10).
Nutrient Acquisition:
Tapeworms hook on to the intestines and absorbs nutrients that have already been broken down by the host's digestive system. Tapeworms do not have digestive systems of their own (3).
Cestodes lack any trace of a digestive tract and therefore must absorb all required substances through their external covering. Before 1960, the body covering of cestodes and trematodes was commonly referred to as a "cuticle", but it is now known that it is a living tissue with high metabolic activity and is synonymous to the term "tegument". Tegumental structure is generally similar in all cestodes studied, differing in details according to species. The tegument is covered by minute projections called microtriches that are underlaid by the tegumental distal cytoplasm. The distal cytoplasm is connected to perikarya by trabeculae that run through superficial muscle layer. The microtriches are similar in some respects to the microvilli found on gut mucosal cells and other vertebrate and invertebrate transport epithelia, and they completely cover the worm's surface, including the suckers. The cytoplasm of the base is continuous with that of the rest of the tegument, and the entire structure is covered by a plasma membrane. A layer of carbohydrate-containing macromolecules, the glycocalyx, is found on the membrane. The microtriches serve to increase the absorptive area of the tegument, but they also may help the worm maintain its position in the host gut. (7, 340/357)
Reproduction and Life cycle:
Segments called "proglottids [are] either male or female", and the tape worm can produce "millions of fertilized eggs" (3). Most tapeworms are hermaphroditic, meaning that an individual contains functional reproductive organs of both sexes. They are usually self-fertilizing. (8)
Sexually mature tapeworms live in the intestine or its diverticulae. A mature tapeworm may live for a few days or up to many years, depending on the species. During its reproductive life, a single worm produces from a few to millions of eggs, each with the potential of developing into the adult form. Because of the great hazards obstructing the course of transmission and development of each worm, mortality is very high. Most tapeworms are hermaphroditic and are capable of fertilizing their own eggs. Sperm transfer is usually from the cirrus to the vagina of the same segment or between adjacent strobilae, if the opportunity permits. A few species of tapeworms are known in which a vagina is absent; hypodermic impregnation has been observed in some of these. In such cases, the cirrus is forced through the body wall, and the sperm are deposited within the parenchyma. How they find their way into the seminal receptacle is unknown. (7,348)
Growth and development:
There are multiple steps in the developmental process of the juvenile forms of tapeworms:
1) Embryogenesis- within the egg to result in a larva, the oncosphere
2) Hatching of the oncosphere after or before being eaten by the next host, where it penetrates to a parenteral site
3) Metamorphosis of the larva in the parenteral site into a juvenile, or metacestode, usually with a scolex
4) The development of the adult from the metacestode in the intestine of the same or another host. The oncospheres of all Eucestoda have thee pairs of hooks, and are thus also referred to as hexacanths.
The free-swimming oncospheres hatching from the egg of some pseudophyllideans and a few trypanorhynchans have a ciliated embryophore and are called coracidia. The larvae of cestodarians have ten hooks and are called decacanths, which are also ciliated and are called lycophoras. (7, 353)
Integument:
The outer layer of the tape worm consists of an epidermis. This layer is made up of a ciliated, cellular epithelium possessing glands and sensory nerve endings. The glands secrete numerous substances, some of which can help trap prey. A basement membrane, or duplicate membrane that separates the epithelium from underlying tissue, provides structure for the organism (6). The tapeworm's outer layer is tough and protective, providing defense from the host's digestive juices (11).
Movement:
Commonly, between the scolex and the strobila lies an undifferentiated zone called the neck, which may be long or short. It contains germinal cells that are responsible for giving rise to new proglottids. Longitudinal muscles are arranged around a central mesenchymal area, largely free of longitudinal fibers. The pattern and development of muscle bundles promote extraordinary mobility. (7, 342)
Sensing the Environment: The scolex contains the chief neural ganglia of the worm, and it bears numerous sensory endings on its anterior surface, likely detecting both physical and chemical stimuli. Such sensory input may allow optimal placement of the scolex and entire strobila with respect to the gut surface and physicochemical gradients within the intestinal milieu. The main nerve center of the cestode is in its scolex, and the complexity of ganglia, commissures, and motor and sensory innervation there depends on the number and complexity of other structures on the scolex. Arising from the cerebral ganglia are a pair of anterior nerves, supplying the apical region of the scolex; four short posterior nerves; and a pair of lateral nerves that continue posteriorly through the strobila. The bothria are innervated by small branches to form the lateral nerves. In addition to the motor innervation of the scolex, there may be sensory endings, particularly at the apex of the tegument. (7, 338/342) Tapeworms have simple eye spots that allow them to distinguish dark from light, and they are aversive to sources of intense light (11).
Gas Exchange: Tapeworms do not have respiratory systems to control gas exchange. Instead, gas is diffused directly across the membranes of their cells. This is possible, for their flat body results in a high surface area to volume ratio (13).
Waste Removal: In cestodes, the main osmoregulatory canals run the length of the strobila from the scolex to the posterior end. These are usually in two pairs, one ventrolateral and the other dorsolateral on each side. The canals may branch and rejoin throghout the strobila or may be independent. Usually a transverse canal joins the ventral canals at the posterior margin of each proglottid. The dorsal and ventral canals unite in the scolex, often with some degree of branching. Posteriorly, the two pairs of canals merge into an excretory bladder with a single pore to the outside. Rarely, the major canals also empty through short, lateral ducts. Although this system is often called the "osmoregulatory", it is also commonly referred to as the "excretory system". (7, 344)
Environmental physiology (temperature, water and salt regulation)
Internal Circulation:
Tapeworms lack a circulatory system. (8)
Chemical Control:
Review Questions:
1. Explain what it means when someone says Tapeworms are hermaphroditic.
2. How do proglottids play into reproduction?
3. How do tapeworms infect two hosts and how do they travel from one to another?
1. http://www.studyblue.com/notes/note/n/lab-pictures-final-/deck/21240
2. http://www.britannica.com/EBchecked/topic/583137/tapeworm
3. http://science.howstuffworks.com/life/human-biology/tapeworm-weight-loss1.htm
4. http://en.wikipedia.org/wiki/Taenia_(genus)
5. http://www.tetrascribe.com/Articles/Tapeworms.pdf
6. http://www.ncsu.edu/project/bio402_315/platyhelminthes/Platyhelminthes%202012.html
7. Foundations of Parasitology, Second Edition, Gerald D. Schmidt / Larry S. Roberts
8. http://www.britannica.com/EBchecked/topic/583137/tapeworm
9. http://www.humanillnesses.com/original/images/hdc_0001_0003_0_img0261.jpg
10. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2683840/
11. http://www.cbv.ns.ca/mchs/diversity/Tapewormpage1.htm
12. http://www.ncsu.edu/project/bio402_315/platyhelminthes/Platyhelminthes%202012.html
13. http://cronodon.com/BioTech/Flatworms.html