Tapeworm Research Paper
Tapeworms are the dominant member of the class Cestoidea. They are ribbon-like, segmented creatures living in the intestines of their vertebrate hosts. There are a dozen orders in this class, most living in fish but two that use humans as hosts. Tapeworms cling to the intestinal wall of their hosts with suckers, hooks, or other adhesive devices. Having no mouth or gut, they receive their nourishment through their skin. Further, they have no type of sensory organs. White or yellowish in color, species in this class vary from 0.04 in (1 mm) long to over 99 ft (30 m).
The broad fish tapeworm (Diphyllobothrium latum), a large tapeworm present in humans, can illustrate the typical life of a tapeworm. As an adult, it attaches itself to the intestinal wall of the human host. Its body, composed of roughly 3,500 sections, probably measures 33-66 ft (10-20 m) long. At this point, it lays about one million eggs each day. Each egg, encased in a thick capsule so that it will not be digested by the host, leaves the host through its feces. When the egg capsule reaches water, an embryo develops and hatches. The larva swims until it is eaten by its first host, a minute …show more content…
crustacean called a copepod. The larva feeds on the copepod and grows. When a fish eats the copepod, the young tapeworm attaches itself to the fish's gut. The tapeworm continues to grow and develop until the fish is eaten by a suitable mammal, such as a human. Only at this point can the tapeworm mature and reproduce.
Read more: Flatworms - Class Cestoidea - Host, Tapeworm, Fish, Living, Life, and Encyclopedia http://science.jrank.org/pages/2735/Flatworms-Class-Cestoidea.html#ixzz1MqFlzX11
Tapeworms are the dominant member of the class Cestoidea. They are ribbon-like, segmented creatures living in the intestines of their vertebrate hosts. There are a dozen orders in this class, most living in fish but two that use humans as hosts. Tapeworms cling to the intestinal wall of their hosts with suckers, hooks, or other adhesive devices. Having no mouth or gut, they receive their nourishment through their skin. Further, they have no type of sensory organs. White or yellowish in color, species in this class vary from 0.04 in (1 mm) long to over 99 ft (30 m).
The broad fish tapeworm (Diphyllobothrium latum), a large tapeworm present in humans, can illustrate the typical life of a tapeworm. As an adult, it attaches itself to the intestinal wall of the human host. Its body, composed of roughly 3,500 sections, probably measures 33-66 ft (10-20 m) long. At this point, it lays about one million eggs each day. Each egg, encased in a thick capsule so that it will not be digested by the host, leaves the host through its feces. When the egg capsule reaches water, an embryo develops and hatches. The larva swims until it is eaten by its first host, a minute crustacean called a copepod. The larva feeds on the copepod and grows. When a fish eats the copepod, the young tapeworm attaches itself to the fish's gut. The tapeworm continues to grow and develop until the fish is eaten by a suitable mammal, such as a human. Only at this point can the tapeworm mature and reproduce.
Read more: Flatworms - Class Cestoidea - Host, Tapeworm, Fish, Living, Life, and Encyclopedia http://science.jrank.org/pages/2735/Flatworms-Class-Cestoidea.html#ixzz1MqFlzX11
Tapeworms are the dominant member of the class Cestoidea. They are ribbon-like, segmented creatures living in the intestines of their vertebrate hosts. There are a dozen orders in this class, most living in fish but two that use humans as hosts. Tapeworms cling to the intestinal wall of their hosts with suckers, hooks, or other adhesive devices. Having no mouth or gut, they receive their nourishment through their skin. Further, they have no type of sensory organs. White or yellowish in color, species in this class vary from 0.04 in (1 mm) long to over 99 ft (30 m).
The broad fish tapeworm (Diphyllobothrium latum), a large tapeworm present in humans, can illustrate the typical life of a tapeworm. As an adult, it attaches itself to the intestinal wall of the human host. Its body, composed of roughly 3,500 sections, probably measures 33-66 ft (10-20 m) long. At this point, it lays about one million eggs each day. Each egg, encased in a thick capsule so that it will not be digested by the host, leaves the host through its feces. When the egg capsule reaches water, an embryo develops and hatches. The larva swims until it is eaten by its first host, a minute crustacean called a copepod. The larva feeds on the copepod and grows. When a fish eats the copepod, the young tapeworm attaches itself to the fish's gut. The tapeworm continues to grow and develop until the fish is eaten by a suitable mammal, such as a human. Only at this point can the tapeworm mature and reproduce.
Read more: Flatworms - Class Cestoidea - Host, Tapeworm, Fish, Living, Life, and Encyclopedia http://science.jrank.org/pages/2735/Flatworms-Class-Cestoidea.html#ixzz1MqFlzX11
The class monogenea is distinguished by most of its members being ectoparasite (meaning they live on the outside of their host's bodies), whereas Digeneans and Cestodes are all endoparasites (meaning they live inside the bodies of their hosts). In order to facilitate their parasitic life style the Monogeneans have complicated attachment organs at the posterior or tail end of their bodies, often including a mixture of suckers, clamps, hooks and spines. Those few species which are endoparasites do not normally venture deeply into their hosts tissues, but live instead in the cloaca or bladder. The Class Monogenea contains animals called monogenetic flukes. Although most of species are ectoparasites on the skin or gills of fish, there a few forms found in the bladders of frogs and even one that lives in the eye of a hippopotamus. The life-cycle of a monogenetic fluke is direct, with a single host. Eggs hatch into ciliated larvae called oncomiracidia that attach to their host or swim around a while before attachment. The oncomiracidium attaches itself to the host via a posterior organ called an opisthaptor, which bears hooks, suckers, clamps, etc. Since they must depend on a single host for both reproduction and transmission, monogenetic flukes have evolved mechanisms that usually ensure that the parasites do not endanger the lives of their hosts, but in crowded conditions (such as fish hatcheries), they can produce serious, damaging infestations.
All trematodes are parasitic, and most adult trematodes parasitize vertebrates. Around 9000 species have been described. Their body is covered with a tegument, a peculiar kind of epidermal arrangement in which the main cell bodies are deep, separated from the cytoplasm that lies next to the exterior by a layer of muscle (but connected to the exterior layer by cellular processes. The exterior layer is syncytial; that is, it is continuous, not broken by cell membranes. The tegument lacks cilia in adults. Unlike monogeneans, trematodes have no opisthoaptor; instead, they are characterized by one or two suckers. They are like turbellarians in having a relatively well developed alimentary canal, and their muscular, excretory, and reproductive systems are also relatively complete. Most trematodes have complex life cycles, with larval stages parasitizing one or more species that are different from host of adults. Larval stages of some medically important species include miracidium, redia, cercaria, and metacercaria. Most trematodes are endoparasites. They include several parasites that have an enormous impact on human populations, such as human liver flukes and the blood flukes that cause schistosomiasis.
The Aspidogastrea is a small group of flukes comprising about 80 species. It belongs to the Trematoda, which comprises the two subclasses Aspidogastrea and Digenea. Species range in length from approximately one mm to several cm. They are parasites of freshwater and marine molluscs and vertebrates (cartilaginous and bony fishes and turtles). Maturation may occur in the mollusc or vertebrate host. None of the species has any economic importance, but the group is of very great interest to biologists because it has several characters which appear to be archaic. Aspidogastreans have a nervous system of extraordinary complexity, greater than that of related free-living forms, and - likewise - they have a very great number of sensory receptors of many different types. Their life cycle is much simpler than that of digenean trematodes, including a mollusc and a facultative or compulsory vertebrate host. There are no multiplicative larval stages in the mollusc host, as known from all digenean trematodes. Furthermore, host specificity of most aspidogastreans is very low, i.e., they infect a wide range of hosts, whereas a typical digenean trematode is restricted to few species (at least of molluscs). Aspidogastreans may survive for many days or even weeks outside a host in simple media (water, saline solution). All this has led to the suggestions that aspidogastreans are archaic trematodes, not yet well adapted to specific hosts, which have given rise to the more "advanced" digenean trematodes, and that the complex life cycles of digenean trematodes have evolved from the simple ones of aspidogastreans.
The Digeneans are a large and successful group of parasites. There are about 6,000 species known to science. They all have complicated life cycles involving at least one intermediate host, which is normally an aquatic snail as well as the primary host which is normally a vertebrate. Digeneans as adults are flat worm shaped animals, the have two sucker. The first is the oral sucker, around the mouth, this has two functions, a) to hold the animal to its host and b) to assist in feeding. The second sucker is found a little way further down the animals body and it has only a single function, that of attachment. Digeneans have what is called an 'alternation of generations' in their life cycle. This means the egg hatches into a larval form, this larval form reproduces asexually to produce numerous copies of itself. eventually these copies change into another larval form which in time grows into a sexually reproducing adult. This possession of an asexual generation means that a single egg can produce not just one infectios agent, but many, maybe even tens or hundreds of thousands. Only about 12 of the 6,000 known species are infectious to mankind, but some of these species are important diseases with of 200 million people infected world wide. The species that infect humans can be divided into groups, the Schistosomiasomes and the non-Schistosomiasomes.
Class Cestoda, include all tapeworms. These flatworms have suckers and teeth that grasp the host in the small head. Behind a short neck are repeated parts of the worm, each containing reproductive structures that contain both eggs and sperm, which can pass out through the host's feces, like fluke eggs. These repeated parts are in order, with the oldest parts farthest away from the head of the tapeworm. The pieces give the worm a ribbonlike structure, beneficial for absorbing nutrients from the intestine, where these parasitic tapeworms live. This class belongs in the phylum Platyhelminthes, consisting of all flatworms. They are more evolved than the Cnidaria because they have bilateral symmetry, with a distinct anterior, posterior, dorsal, and ventral end, with a defined head. However, flatworms lack a body cavity, a fluid filled region between the epidermis and the digestive tract. Flatworms also lack a complete digestive tract, but instead only have one opening for substances to both enter and leave the body. This is because the gastrula opening in the development of a flatworm never fully evolves into a hole in the anterior and posterior end. The Cestoda is the class of tapeworms, parasitic flatworms that live as adults in the digestive tracts of vertebrates. They have a round head called a "scolex" with hooks and suckers for attachment. Posterior to the scolex, they have proglottids (immature, mature, gravid) that contain numerous eggs. The proglottid is the sac of sex organs. Not having defined digestive tract, they absorb food predigested by the host. Mature proglottids are released from the mature tapeworm and leave the host in its feces. For example, human feces contaminate the food of intermediate host, such as pigs or cattle, and the tapeworm eggs develop into larvae (cysticercus). Humans can get larvae of tapeworms by eating uncooked meat. This tapeworm is often referred to as a "bladderworm." It is shaped thin like a strip of tape unlike the rounded earthworm. The large tapeworms can be 20m or longer and they can be harmful to humans.
Characteristics of Nemertea:- 1)Bilaterally symmetrical and dorsoventrally flattened. 2)Body has more than two layers of cells with tissues and organs. 3)Body has a through gut with a mouth and anus. 4)Body has no body cavity. 5)Has a blood system with blood vessels. 6)Has a well developed nervous system and a brain. 7)Has an eversible and retractable ectodermal proboscis. 8)Reproduction is by asexual fragmentation, or sexual, when it is normally gonochoristic. 9)Most species are carnivorous and predatory. 10)Most are aquatic and marine, there are some terrestrial and freshwater forms. Nemertea is a phylum of invertebrate animals also known as ribbon worms or proboscis worms. Alternative names for the phylum have included Nemertini, Nemertinea and Rhynchocoela. Although most are less than 20 centimetres (7.9in) long, one specimen has been estimated at 54 metres (177ft), which would make it the longest animal ever found. Most are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many have patterns of yellow, orange, red and green coloration. The foregut, stomach and intestine run a little below the midline of the body, the anus is at the tip of the tail, and the mouth is under the front. A little above the gut is the rhynchocoel, a cavity which mostly runs above the midline and ends a little short of the rear of the body. All species have a proboscis which lies in the rhynchocoel when inactive but everts (turns inside-out) to emerge just above the mouth and capture the animal's prey with poisons. A very stretchy muscle in the back of the rhynchocoel pulls the proboscis in when an attack ends. A few species with stubby bodies filter feed and have suckers at the front and back ends, with which they attach to a host. | | | |
Gastrotrichs are small 0.5mm to 4mm in length, generally colourless worms that are related to both nematodes and tubellarian flatworms. They are free living in aquatic environments, either marine or freshwater and feed on a variety of living and dead organic matter, anything small enough to be swept into their mouths by the 4 tufts of beating cilia on the head. They have very short lives, from 3 to 21 days and are not terribly important economically though as with all living things they are part of the food and predator webs of other aquatic organisms. They have from 2 to 250 adhesive tubes on the lower sides of their bodies which help them to temporarily attach themselves to vegetation or other submerged surfaces. There are about 400 species known to science. Gastrotrichs are either hermaphroditic or parthenogenetic. Most marine species are hermaphroditic possessing both male and female gonads, though only one set is functional at a time, so an individual is either functionally a female or functionally a male. Sperm is transferred from a functionally male Gastrotrich to a functionally female one via a spermatophore. Only a small number of eggs are produced at any one time and the young hatch out as small Gastrotrichs, there is no larval stage. The young feed and grow quickly and may reach sexual maturity in as little as 2 days. Freshwater species are nearly all parthenogenetic, meaning they are all females. They produce two sorts of eggs, a tough overwintering egg which need to experience drought, excessive heat or excessive cold before they will germinate. These eggs allow the species to exist in unstable environments, the second sort of eggs hatch almost immediately to produce small Gastrotrichs as in marine species.
Characteristics of Rotifera:- 1)Bilaterally symmetrical. 2)Body has more than two cell layers, tissues and organs. 3)Body cavity is a pseudocoelom. 4)Body possesses a through gut with an anus. 5)Body covered in an external layer of chitin called a lorica. 6)Has a nervous system with a brain and paired nerves. 7)Has no circulatory or respiratory organs. 8)Reproduction mostly parthenogenetic, otherwise sexual and gonochoristic. 9)Feed on bacteria, and protista, or are parasitic. 10)All live in aquatic environments either free swimming or attached. |
The Kinorhynchan body is comprised of a head, a neck, and a trunk, the trunk has 11 segments or zonites each with a single dorsal plate (tergite), and two ventral plates (sternites). The head which bears the recurved spines or scalids can be retracted into the trunk and is therefore called an 'introvert'. The head also bears an oral cone or mouth surrounded by more spines called stylets. The gut passes straight along the body and their is an anus at the posterior (tail) end of the body. Metabolic excretion and water balance are performed by a pair of protonephridia in the 10th zonite, wastes are eliminated through duct opening through the 11th zonite called a nephridiopore. Kinorhynchans have a reasonably well developed nervous system composed of a nerve ring or brain which encircles the anterior (front) end of the pharynx, a double nerve cord which runs down the ventral side of the body and various other nerves and ganglia.
Kinorhyncha are not a very speciose phyla with only about 150 species currently known to science. They live in marine sediments ranging from coastal to depths of up to 5000 metres and have been found in all the worlds seas and oceans. They can not swim, and move by pushing their heads forward into the mud, extending their scalids then retracting the head into the body, because the head is held in place by the spines this has the effect of dragging the body forward. the spines can then be closed and the head pushed forward once more. They feed on diatoms and other organic matter they find in the mud.
The Kinorhyncha have the two sexes separate though to us they often look the same.
Very little is know of their reproduction, the eggs are eventually fertilised, perhaps by a spermatophore attached to the females cuticle. The larvae are free living and go through at least 6 moults of their cuticle before they reach maturity. The eggs take from 15 to 80 days to hatch. The larvae are free swimming and look like the Kinorhyncha with scalid spines around their heads and a set of oral stylets that can be everted or retracted into the body cavity, and not at all like their parents. They are parasites of invertebrates, though not necessarily aquatic ones. The larvae have a better developed digestive system than the adults but it is likely they derive most of their nutrition from nutrients absorbed through their body
wall.
Development of the larvae can takes from a few weeks to several months, and there can be several generations per year. It is assumed that the mature larvae somehow manipulate their non-aquatic hosts into seeking out water, though how this is accomplished is unknown. Most species inhabit freshwater, there is one marine genus which parasitises crabs. In some species, individuals that mature in autumn form cysts on grass near to water and wait until spring before continuing their lives.
Free living nematodes are long thin worms with transparent and typically curled bodies, parasitic species have a variety of less streamline shapes relating to their degenerate parasitic life styles, one unifying characteristic that makes the phylum unique is the lack of cilia or flagella, even the sperm of nematodes are amoeboid. Nematodes as parasites have been known for a long time and the earliest recorded literary mention of them is an Egyptian papyrus from 1500 BC
Nematodes live in a vast variety of habitats, ecologically they can be divided into free living forms and parasitic forms. Free living forms have a simple life cycle involving 4 juvenile instars on the path from egg to adult. Parasitic species have developed a wide range of variations on this basic theme. The variations involve whether there is a secondary host and the amount of time spent in one or either hosts. There is also considerable variability in the way that they move from one host species to another. thus while many species lay eggs that pass out of the primary host with the faeces where they are eaten by the secondary host which then gets eaten in turn by the primary host after the Nematodes have developed. Because it is not always totally reliable that the secondary host will be eaten just as the Nematode larvae have developed into the infective stage many species have the ability to encyst themselves in the muscle or cuticle of their secondary hosts.
Nematomorph's are closely related to the nematodes, and like them they move by muscularly induced undulating waves passing along the body. The adults do not feed, nor do they live long. Their only function in the life of the species is reproduction. Females are normally sedentary and are searched for by the more active males who curl themselves around the females and deposit a spermatophore near the females cloaca. The sperm then swim into the females seminal receptacle from where they can later fertilise her eggs. The female deposits her eggs in long strings, all stuck together and tangled around aquatic plants.
Acanthocephalans come in male and female and unusually for invertebrates the males have a penis and the females have a vagina and the first step in the reproductive cycle is copulation, which occurs in the vertebrate hosts guts. Males also have a cement gland which they use to seal the females vagina after copulation. The eggs are fertilised by the sperm within the females body and embryonic development occurs their as well. After a certain stage of development the larvae become encapsulated and these 'shelled' or 'encased' larvae are called Acanthors and they are released by the female in to the hosts guts where they pass out with the faeces. They then remain dormant until eaten by the secondary, or intermediary host. Once inside the secondary hosts guts they hatch into a second stage larvae called an Acanthella, as which they grow. After reaching their full size they encyst themselves in their secondary hosts tissues where they remain dormant until the secondary host is eaten by the primary host. This encysted stage is called a Cystacanth. Many acanthocephalan primary hosts are carnivores, or at least omnivores as this helps ensure the fulfilling of the life cycle by increasing the chances of the secondary host being eaten by the primary host. Some species manage to change the habits of their secondary host to make it more likely that it is eaten, by making it stay out in the open for instance.
Loricifera is a phylum of very small to microscopic marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more that have been collected and not yet described. Their size ranges from 100 µm to ca. 1mm. They are characterised by a protective outer case called a lorica and their habitat, which is in the spaces between marine gravel to which they attach themselves. The phylum was discovered in 1983 by Reinhardt Kristensen, in Roscoff, France. They are among the most recently discovered groups of Metazoans. They attach themselves quite firmly to the substratum, and hence remained undiscovered for so long. The first specimen was collected in the 1970s, and later described in 1983. They are found at all depths, in different sediment types, and in all latitudes.
The Priapulida, or Priapula are a small phylum (about 16 species known to scientists) of normally small worm like animals. They range in length from 0.5 mm for species of Tubuluchus to around 200 mm for species of Priapulus. They occur in most seas, both tropical and polar, at a variety of depths, from shallow coastal waters to as far down as 7,200 metres. The name Priapulida refers to the fact that the scientists who first named them thought they looked like a human penis, however they look more like some species of cacti and it would not be unreasonable to use the term Cactus Worms as their common name. All known species are marine and benthic (meaning they live in or on the sea floor). The priapulid body consists of two parts; a prosoma, sometimes called an introvert, and a trunk. The prosoma can be drawn into the trunk which is why it is sometimes called the introvert. The prosoma has the mouth at its anterior end. The mouth has 5 spines, called scalids arranged around its opening. There are also rows of scalids running down the prosoma in most species. The trunk also often has spines or scales and may have, as in the case of the genus Priapulus, caudal appendages (which look like a bundle of worms at the end of the animals body). These are suspected of having a respiratory function. The trunk bears 20 to 30 external annuli (rings) but there is no internal segmentation. The body has a cuticle which contains chitin as well as other materials which lies outside of the epidermis. This cuticle is moulted as the animal grows. The body cavity of priapulids is a true coelom, or a pseudocoelom, depending on which authority you consult. Embryology is little studies in these inoffensive creatures, and it is a detailed study of this which will answer the question. Behind the mouth is a pharynx which leads to a short straight gut which ends in an anus at the posterior (tail) end of the animal's body.
The broad fish tapeworm (Diphyllobothrium latum), a large tapeworm present in humans, can illustrate the typical life of a tapeworm. As an adult, it attaches itself to the intestinal wall of the human host. Its body, composed of roughly 3,500 sections, probably measures 33-66 ft (10-20 m) long. At this point, it lays about one million eggs each day. Each egg, encased in a thick capsule so that it will not be digested by the host, leaves the host through its feces. When the egg capsule reaches water, an embryo develops and hatches. The larva swims until it is eaten by its first host, a minute …show more content…
crustacean called a copepod. The larva feeds on the copepod and grows. When a fish eats the copepod, the young tapeworm attaches itself to the fish's gut. The tapeworm continues to grow and develop until the fish is eaten by a suitable mammal, such as a human. Only at this point can the tapeworm mature and reproduce.
Read more: Flatworms - Class Cestoidea - Host, Tapeworm, Fish, Living, Life, and Encyclopedia http://science.jrank.org/pages/2735/Flatworms-Class-Cestoidea.html#ixzz1MqFlzX11
Tapeworms are the dominant member of the class Cestoidea. They are ribbon-like, segmented creatures living in the intestines of their vertebrate hosts. There are a dozen orders in this class, most living in fish but two that use humans as hosts. Tapeworms cling to the intestinal wall of their hosts with suckers, hooks, or other adhesive devices. Having no mouth or gut, they receive their nourishment through their skin. Further, they have no type of sensory organs. White or yellowish in color, species in this class vary from 0.04 in (1 mm) long to over 99 ft (30 m).
The broad fish tapeworm (Diphyllobothrium latum), a large tapeworm present in humans, can illustrate the typical life of a tapeworm. As an adult, it attaches itself to the intestinal wall of the human host. Its body, composed of roughly 3,500 sections, probably measures 33-66 ft (10-20 m) long. At this point, it lays about one million eggs each day. Each egg, encased in a thick capsule so that it will not be digested by the host, leaves the host through its feces. When the egg capsule reaches water, an embryo develops and hatches. The larva swims until it is eaten by its first host, a minute crustacean called a copepod. The larva feeds on the copepod and grows. When a fish eats the copepod, the young tapeworm attaches itself to the fish's gut. The tapeworm continues to grow and develop until the fish is eaten by a suitable mammal, such as a human. Only at this point can the tapeworm mature and reproduce.
Read more: Flatworms - Class Cestoidea - Host, Tapeworm, Fish, Living, Life, and Encyclopedia http://science.jrank.org/pages/2735/Flatworms-Class-Cestoidea.html#ixzz1MqFlzX11
Tapeworms are the dominant member of the class Cestoidea. They are ribbon-like, segmented creatures living in the intestines of their vertebrate hosts. There are a dozen orders in this class, most living in fish but two that use humans as hosts. Tapeworms cling to the intestinal wall of their hosts with suckers, hooks, or other adhesive devices. Having no mouth or gut, they receive their nourishment through their skin. Further, they have no type of sensory organs. White or yellowish in color, species in this class vary from 0.04 in (1 mm) long to over 99 ft (30 m).
The broad fish tapeworm (Diphyllobothrium latum), a large tapeworm present in humans, can illustrate the typical life of a tapeworm. As an adult, it attaches itself to the intestinal wall of the human host. Its body, composed of roughly 3,500 sections, probably measures 33-66 ft (10-20 m) long. At this point, it lays about one million eggs each day. Each egg, encased in a thick capsule so that it will not be digested by the host, leaves the host through its feces. When the egg capsule reaches water, an embryo develops and hatches. The larva swims until it is eaten by its first host, a minute crustacean called a copepod. The larva feeds on the copepod and grows. When a fish eats the copepod, the young tapeworm attaches itself to the fish's gut. The tapeworm continues to grow and develop until the fish is eaten by a suitable mammal, such as a human. Only at this point can the tapeworm mature and reproduce.
Read more: Flatworms - Class Cestoidea - Host, Tapeworm, Fish, Living, Life, and Encyclopedia http://science.jrank.org/pages/2735/Flatworms-Class-Cestoidea.html#ixzz1MqFlzX11
The class monogenea is distinguished by most of its members being ectoparasite (meaning they live on the outside of their host's bodies), whereas Digeneans and Cestodes are all endoparasites (meaning they live inside the bodies of their hosts). In order to facilitate their parasitic life style the Monogeneans have complicated attachment organs at the posterior or tail end of their bodies, often including a mixture of suckers, clamps, hooks and spines. Those few species which are endoparasites do not normally venture deeply into their hosts tissues, but live instead in the cloaca or bladder. The Class Monogenea contains animals called monogenetic flukes. Although most of species are ectoparasites on the skin or gills of fish, there a few forms found in the bladders of frogs and even one that lives in the eye of a hippopotamus. The life-cycle of a monogenetic fluke is direct, with a single host. Eggs hatch into ciliated larvae called oncomiracidia that attach to their host or swim around a while before attachment. The oncomiracidium attaches itself to the host via a posterior organ called an opisthaptor, which bears hooks, suckers, clamps, etc. Since they must depend on a single host for both reproduction and transmission, monogenetic flukes have evolved mechanisms that usually ensure that the parasites do not endanger the lives of their hosts, but in crowded conditions (such as fish hatcheries), they can produce serious, damaging infestations.
All trematodes are parasitic, and most adult trematodes parasitize vertebrates. Around 9000 species have been described. Their body is covered with a tegument, a peculiar kind of epidermal arrangement in which the main cell bodies are deep, separated from the cytoplasm that lies next to the exterior by a layer of muscle (but connected to the exterior layer by cellular processes. The exterior layer is syncytial; that is, it is continuous, not broken by cell membranes. The tegument lacks cilia in adults. Unlike monogeneans, trematodes have no opisthoaptor; instead, they are characterized by one or two suckers. They are like turbellarians in having a relatively well developed alimentary canal, and their muscular, excretory, and reproductive systems are also relatively complete. Most trematodes have complex life cycles, with larval stages parasitizing one or more species that are different from host of adults. Larval stages of some medically important species include miracidium, redia, cercaria, and metacercaria. Most trematodes are endoparasites. They include several parasites that have an enormous impact on human populations, such as human liver flukes and the blood flukes that cause schistosomiasis.
The Aspidogastrea is a small group of flukes comprising about 80 species. It belongs to the Trematoda, which comprises the two subclasses Aspidogastrea and Digenea. Species range in length from approximately one mm to several cm. They are parasites of freshwater and marine molluscs and vertebrates (cartilaginous and bony fishes and turtles). Maturation may occur in the mollusc or vertebrate host. None of the species has any economic importance, but the group is of very great interest to biologists because it has several characters which appear to be archaic. Aspidogastreans have a nervous system of extraordinary complexity, greater than that of related free-living forms, and - likewise - they have a very great number of sensory receptors of many different types. Their life cycle is much simpler than that of digenean trematodes, including a mollusc and a facultative or compulsory vertebrate host. There are no multiplicative larval stages in the mollusc host, as known from all digenean trematodes. Furthermore, host specificity of most aspidogastreans is very low, i.e., they infect a wide range of hosts, whereas a typical digenean trematode is restricted to few species (at least of molluscs). Aspidogastreans may survive for many days or even weeks outside a host in simple media (water, saline solution). All this has led to the suggestions that aspidogastreans are archaic trematodes, not yet well adapted to specific hosts, which have given rise to the more "advanced" digenean trematodes, and that the complex life cycles of digenean trematodes have evolved from the simple ones of aspidogastreans.
The Digeneans are a large and successful group of parasites. There are about 6,000 species known to science. They all have complicated life cycles involving at least one intermediate host, which is normally an aquatic snail as well as the primary host which is normally a vertebrate. Digeneans as adults are flat worm shaped animals, the have two sucker. The first is the oral sucker, around the mouth, this has two functions, a) to hold the animal to its host and b) to assist in feeding. The second sucker is found a little way further down the animals body and it has only a single function, that of attachment. Digeneans have what is called an 'alternation of generations' in their life cycle. This means the egg hatches into a larval form, this larval form reproduces asexually to produce numerous copies of itself. eventually these copies change into another larval form which in time grows into a sexually reproducing adult. This possession of an asexual generation means that a single egg can produce not just one infectios agent, but many, maybe even tens or hundreds of thousands. Only about 12 of the 6,000 known species are infectious to mankind, but some of these species are important diseases with of 200 million people infected world wide. The species that infect humans can be divided into groups, the Schistosomiasomes and the non-Schistosomiasomes.
Class Cestoda, include all tapeworms. These flatworms have suckers and teeth that grasp the host in the small head. Behind a short neck are repeated parts of the worm, each containing reproductive structures that contain both eggs and sperm, which can pass out through the host's feces, like fluke eggs. These repeated parts are in order, with the oldest parts farthest away from the head of the tapeworm. The pieces give the worm a ribbonlike structure, beneficial for absorbing nutrients from the intestine, where these parasitic tapeworms live. This class belongs in the phylum Platyhelminthes, consisting of all flatworms. They are more evolved than the Cnidaria because they have bilateral symmetry, with a distinct anterior, posterior, dorsal, and ventral end, with a defined head. However, flatworms lack a body cavity, a fluid filled region between the epidermis and the digestive tract. Flatworms also lack a complete digestive tract, but instead only have one opening for substances to both enter and leave the body. This is because the gastrula opening in the development of a flatworm never fully evolves into a hole in the anterior and posterior end. The Cestoda is the class of tapeworms, parasitic flatworms that live as adults in the digestive tracts of vertebrates. They have a round head called a "scolex" with hooks and suckers for attachment. Posterior to the scolex, they have proglottids (immature, mature, gravid) that contain numerous eggs. The proglottid is the sac of sex organs. Not having defined digestive tract, they absorb food predigested by the host. Mature proglottids are released from the mature tapeworm and leave the host in its feces. For example, human feces contaminate the food of intermediate host, such as pigs or cattle, and the tapeworm eggs develop into larvae (cysticercus). Humans can get larvae of tapeworms by eating uncooked meat. This tapeworm is often referred to as a "bladderworm." It is shaped thin like a strip of tape unlike the rounded earthworm. The large tapeworms can be 20m or longer and they can be harmful to humans.
Characteristics of Nemertea:- 1)Bilaterally symmetrical and dorsoventrally flattened. 2)Body has more than two layers of cells with tissues and organs. 3)Body has a through gut with a mouth and anus. 4)Body has no body cavity. 5)Has a blood system with blood vessels. 6)Has a well developed nervous system and a brain. 7)Has an eversible and retractable ectodermal proboscis. 8)Reproduction is by asexual fragmentation, or sexual, when it is normally gonochoristic. 9)Most species are carnivorous and predatory. 10)Most are aquatic and marine, there are some terrestrial and freshwater forms. Nemertea is a phylum of invertebrate animals also known as ribbon worms or proboscis worms. Alternative names for the phylum have included Nemertini, Nemertinea and Rhynchocoela. Although most are less than 20 centimetres (7.9in) long, one specimen has been estimated at 54 metres (177ft), which would make it the longest animal ever found. Most are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many have patterns of yellow, orange, red and green coloration. The foregut, stomach and intestine run a little below the midline of the body, the anus is at the tip of the tail, and the mouth is under the front. A little above the gut is the rhynchocoel, a cavity which mostly runs above the midline and ends a little short of the rear of the body. All species have a proboscis which lies in the rhynchocoel when inactive but everts (turns inside-out) to emerge just above the mouth and capture the animal's prey with poisons. A very stretchy muscle in the back of the rhynchocoel pulls the proboscis in when an attack ends. A few species with stubby bodies filter feed and have suckers at the front and back ends, with which they attach to a host. | | | |
Gastrotrichs are small 0.5mm to 4mm in length, generally colourless worms that are related to both nematodes and tubellarian flatworms. They are free living in aquatic environments, either marine or freshwater and feed on a variety of living and dead organic matter, anything small enough to be swept into their mouths by the 4 tufts of beating cilia on the head. They have very short lives, from 3 to 21 days and are not terribly important economically though as with all living things they are part of the food and predator webs of other aquatic organisms. They have from 2 to 250 adhesive tubes on the lower sides of their bodies which help them to temporarily attach themselves to vegetation or other submerged surfaces. There are about 400 species known to science. Gastrotrichs are either hermaphroditic or parthenogenetic. Most marine species are hermaphroditic possessing both male and female gonads, though only one set is functional at a time, so an individual is either functionally a female or functionally a male. Sperm is transferred from a functionally male Gastrotrich to a functionally female one via a spermatophore. Only a small number of eggs are produced at any one time and the young hatch out as small Gastrotrichs, there is no larval stage. The young feed and grow quickly and may reach sexual maturity in as little as 2 days. Freshwater species are nearly all parthenogenetic, meaning they are all females. They produce two sorts of eggs, a tough overwintering egg which need to experience drought, excessive heat or excessive cold before they will germinate. These eggs allow the species to exist in unstable environments, the second sort of eggs hatch almost immediately to produce small Gastrotrichs as in marine species.
Characteristics of Rotifera:- 1)Bilaterally symmetrical. 2)Body has more than two cell layers, tissues and organs. 3)Body cavity is a pseudocoelom. 4)Body possesses a through gut with an anus. 5)Body covered in an external layer of chitin called a lorica. 6)Has a nervous system with a brain and paired nerves. 7)Has no circulatory or respiratory organs. 8)Reproduction mostly parthenogenetic, otherwise sexual and gonochoristic. 9)Feed on bacteria, and protista, or are parasitic. 10)All live in aquatic environments either free swimming or attached. |
The Kinorhynchan body is comprised of a head, a neck, and a trunk, the trunk has 11 segments or zonites each with a single dorsal plate (tergite), and two ventral plates (sternites). The head which bears the recurved spines or scalids can be retracted into the trunk and is therefore called an 'introvert'. The head also bears an oral cone or mouth surrounded by more spines called stylets. The gut passes straight along the body and their is an anus at the posterior (tail) end of the body. Metabolic excretion and water balance are performed by a pair of protonephridia in the 10th zonite, wastes are eliminated through duct opening through the 11th zonite called a nephridiopore. Kinorhynchans have a reasonably well developed nervous system composed of a nerve ring or brain which encircles the anterior (front) end of the pharynx, a double nerve cord which runs down the ventral side of the body and various other nerves and ganglia.
Kinorhyncha are not a very speciose phyla with only about 150 species currently known to science. They live in marine sediments ranging from coastal to depths of up to 5000 metres and have been found in all the worlds seas and oceans. They can not swim, and move by pushing their heads forward into the mud, extending their scalids then retracting the head into the body, because the head is held in place by the spines this has the effect of dragging the body forward. the spines can then be closed and the head pushed forward once more. They feed on diatoms and other organic matter they find in the mud.
The Kinorhyncha have the two sexes separate though to us they often look the same.
Very little is know of their reproduction, the eggs are eventually fertilised, perhaps by a spermatophore attached to the females cuticle. The larvae are free living and go through at least 6 moults of their cuticle before they reach maturity. The eggs take from 15 to 80 days to hatch. The larvae are free swimming and look like the Kinorhyncha with scalid spines around their heads and a set of oral stylets that can be everted or retracted into the body cavity, and not at all like their parents. They are parasites of invertebrates, though not necessarily aquatic ones. The larvae have a better developed digestive system than the adults but it is likely they derive most of their nutrition from nutrients absorbed through their body
wall.
Development of the larvae can takes from a few weeks to several months, and there can be several generations per year. It is assumed that the mature larvae somehow manipulate their non-aquatic hosts into seeking out water, though how this is accomplished is unknown. Most species inhabit freshwater, there is one marine genus which parasitises crabs. In some species, individuals that mature in autumn form cysts on grass near to water and wait until spring before continuing their lives.
Free living nematodes are long thin worms with transparent and typically curled bodies, parasitic species have a variety of less streamline shapes relating to their degenerate parasitic life styles, one unifying characteristic that makes the phylum unique is the lack of cilia or flagella, even the sperm of nematodes are amoeboid. Nematodes as parasites have been known for a long time and the earliest recorded literary mention of them is an Egyptian papyrus from 1500 BC
Nematodes live in a vast variety of habitats, ecologically they can be divided into free living forms and parasitic forms. Free living forms have a simple life cycle involving 4 juvenile instars on the path from egg to adult. Parasitic species have developed a wide range of variations on this basic theme. The variations involve whether there is a secondary host and the amount of time spent in one or either hosts. There is also considerable variability in the way that they move from one host species to another. thus while many species lay eggs that pass out of the primary host with the faeces where they are eaten by the secondary host which then gets eaten in turn by the primary host after the Nematodes have developed. Because it is not always totally reliable that the secondary host will be eaten just as the Nematode larvae have developed into the infective stage many species have the ability to encyst themselves in the muscle or cuticle of their secondary hosts.
Nematomorph's are closely related to the nematodes, and like them they move by muscularly induced undulating waves passing along the body. The adults do not feed, nor do they live long. Their only function in the life of the species is reproduction. Females are normally sedentary and are searched for by the more active males who curl themselves around the females and deposit a spermatophore near the females cloaca. The sperm then swim into the females seminal receptacle from where they can later fertilise her eggs. The female deposits her eggs in long strings, all stuck together and tangled around aquatic plants.
Acanthocephalans come in male and female and unusually for invertebrates the males have a penis and the females have a vagina and the first step in the reproductive cycle is copulation, which occurs in the vertebrate hosts guts. Males also have a cement gland which they use to seal the females vagina after copulation. The eggs are fertilised by the sperm within the females body and embryonic development occurs their as well. After a certain stage of development the larvae become encapsulated and these 'shelled' or 'encased' larvae are called Acanthors and they are released by the female in to the hosts guts where they pass out with the faeces. They then remain dormant until eaten by the secondary, or intermediary host. Once inside the secondary hosts guts they hatch into a second stage larvae called an Acanthella, as which they grow. After reaching their full size they encyst themselves in their secondary hosts tissues where they remain dormant until the secondary host is eaten by the primary host. This encysted stage is called a Cystacanth. Many acanthocephalan primary hosts are carnivores, or at least omnivores as this helps ensure the fulfilling of the life cycle by increasing the chances of the secondary host being eaten by the primary host. Some species manage to change the habits of their secondary host to make it more likely that it is eaten, by making it stay out in the open for instance.
Loricifera is a phylum of very small to microscopic marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more that have been collected and not yet described. Their size ranges from 100 µm to ca. 1mm. They are characterised by a protective outer case called a lorica and their habitat, which is in the spaces between marine gravel to which they attach themselves. The phylum was discovered in 1983 by Reinhardt Kristensen, in Roscoff, France. They are among the most recently discovered groups of Metazoans. They attach themselves quite firmly to the substratum, and hence remained undiscovered for so long. The first specimen was collected in the 1970s, and later described in 1983. They are found at all depths, in different sediment types, and in all latitudes.
The Priapulida, or Priapula are a small phylum (about 16 species known to scientists) of normally small worm like animals. They range in length from 0.5 mm for species of Tubuluchus to around 200 mm for species of Priapulus. They occur in most seas, both tropical and polar, at a variety of depths, from shallow coastal waters to as far down as 7,200 metres. The name Priapulida refers to the fact that the scientists who first named them thought they looked like a human penis, however they look more like some species of cacti and it would not be unreasonable to use the term Cactus Worms as their common name. All known species are marine and benthic (meaning they live in or on the sea floor). The priapulid body consists of two parts; a prosoma, sometimes called an introvert, and a trunk. The prosoma can be drawn into the trunk which is why it is sometimes called the introvert. The prosoma has the mouth at its anterior end. The mouth has 5 spines, called scalids arranged around its opening. There are also rows of scalids running down the prosoma in most species. The trunk also often has spines or scales and may have, as in the case of the genus Priapulus, caudal appendages (which look like a bundle of worms at the end of the animals body). These are suspected of having a respiratory function. The trunk bears 20 to 30 external annuli (rings) but there is no internal segmentation. The body has a cuticle which contains chitin as well as other materials which lies outside of the epidermis. This cuticle is moulted as the animal grows. The body cavity of priapulids is a true coelom, or a pseudocoelom, depending on which authority you consult. Embryology is little studies in these inoffensive creatures, and it is a detailed study of this which will answer the question. Behind the mouth is a pharynx which leads to a short straight gut which ends in an anus at the posterior (tail) end of the animal's body.