Class Turbellaria: free-living flatworms (Planaria).Class Monogenea: monogenetic flukes (one generation in their life cycle).Class Trematoda: digenetic flukes (Clonorchis, Fasciola, Schistosoma, Paragonimus).Class Cestoda: tapeworms (Diplydium, Taenia).

You are watching: An endoparasitic acoelomate with a body consisting of a scolex and a series of proglottids is a

Phylum Rotifera: rotifersPhylum Acanthocephala: spiny-headed wormsPhylum Ectoprocta (Bryozoa) – “moss animals” (Bugula, Plumatella)Phylum Brachiopoda – “lampshells” (Lingula, Terebratella)

Phylum native this point on, all animals covered in the Zoo lab website have actually primary bilateral symmetry and also are triploblastic, the is, 3 true germ class (the ectoderm, mesoderm and also endoderm) room formed throughout gastrulation of the blastula phase of development. If radial symmetry may be fine suited because that sessile or slow-moving forms, pets that are energetic in search food, shelter and also mates call for a brand-new body plan. Bilateral the contrary coupled with cephalization solves this problems. The anterior finish moves forward and also the posterior follows. The dorsal next is kept dealing with up and also the ventral side is preserved down and also usually devoted for locomotion.The bilateral grade of metazoans is further subdivided right into two key divisions: the protostomes and also deuterostomes, which space separated ~ above the basis of a variety of embryological differences. Evidence from sequence analysis of the small-subunit ribosomal gene suggests that some time after ancestral deuterostomes and also protostomes sail from one another during the Cambrian period, protostomes break-up into two big groups (superphyla), the Ecdysozoa and Lophotrochozoa. In this lab we will research one acoelomate lophotrochozoan phylum and several smaller pseudocoelomate and eucoelomate lophotrochozoan phyla.

The Phylum Platyhelminthes has over 20,000 free-living and parasitic species of acoelomate pets called flatworms. In flatworms, the body the is flattened dorsoventrally, with the mouth and also genital pore usually situated in a ventral position. The room between the gut and outside is filled through mesodermal muscle fibers and undifferentiated parenchyma. Return fluid-filled spaces in the parenchyma offer as a hydrostatic skeleton because that support and also to help in inner transport, the pets lack a human body cavity, i beg your pardon is why lock are referred to as acoelomate. Most free-living flatworms have actually a gastrovascular-type digestive system (a mouth is present however no anus), if parasitic forms generally have actually no digestive system.Flatworms have a centralized nervous mechanism consisting the pair of cerebral ganglia and longitudinal nerve cords linked to transverse nerves. The excretory system (absent in part forms) consists of two lateral canals v protonephridia bearing fire cells. Although many flatworms room free-living, the phylum includes some an extremely important parasitic species as well.In terms of reproduction, flatworms have the right to reproduce sexually or asexually. Most varieties are monoecious but practice cross fertilization. Countless freshwater turbellarians have the right to reproduce asexually through fission in i beg your pardon the animal simply divides right into two halves, each of i beg your pardon regenerates the other half. In some turbellarians (as that is in many other animals), the yolk that provides nutrition because that the arising embryo is containing in ~ the egg cell itself, a condition described together endolecithal. In the monogeneans, trematodes and cestodes (as well together in a couple of turbellarians), yolk is contributed by cell released native organs dubbed yolk glands, and also the egg are therefore described together ectolecithal. Development may be direct or indirect.

The class Turbellaria includes mostly free-living creates ranging in size from a few mm to 50 cm. Most species are bottom dwellers in marine and freshwater environments that crawl end rocks, sand or vegetation. Smaller forms can swimming by method of ventral cilia, but more often they move by laying down a paper of mucus that aids in adhesion and helps the cilia gain traction. Larger develops use an effective muscle contractions come crawl or swim. Distinctive to turbellarians are rod-shaped rhabdites found amongst the ventral epidermal cell of the human body surface. This rhabdites secrete mucus the coats the animal"s body, possibly for protection versus predators or to protect against drying.In terms of nutrition, many turbellarians space predators and also scavengers. Epidermal mucous secretions trap and kill food items. A muscular pharynx everted though the ventral mouth is used to secrete cradle enzymes into prey, i beg your pardon is climate sucked into the branched intestine that develops a gastrovascular cavity. In enhancement to a an easy nervous system, turbellarians have light-sensitive eye spots called ocelli that help orient the animal to the direction that light. Touch and chemical receptor in some forms like the planarian seen in rap are concentrated in lateral projections from the head referred to as auricles the look favor ear lobes. Reproduction in turbellarians can take place asexually through fission or sexually; all develops are monoecious but practice cross-fertilization. Planarians are also known for their tremendous powers the regeneration, and a planarian that has been reduced into 3 pieces will provide rise come three new complete individuals!

The course Monogenea contains animals called monogenetic flukes. Although many of species are ectoparasites ~ above the skin or gills that fish, over there a couple of forms discovered in the bladders of frogs and also even one that resides in the eye the a hippopotamus! The life bicycle of a monogenetic fluke is direct, through a single host. Since they must depend ~ above a solitary host because that both reproduction and transmission, monogenetic flukes have developed mechanisms that generally ensure the the parasites execute not endanger the lives of your hosts, however in crowded conditions (such together fish hatcheries), lock can develop serious, damaging infestations.

The class Trematoda contains about 8,000 types of leaf-like pets called digenetic flukes. The adults room endoparasites ~ above vertebrates yet many invertebrates serve as intermediary hosts, and also many species of medical and economic importance! breakthrough is trematodes indirect; not only adults but larvae reproduce and all varieties have at least two hosts, one because that transmission and also the other for reproduction. The vast bulk of flukes own two big suckers that are supplied for attachment, one anterior one dubbed an dental sucker, which surround the mouth and a posterior one dubbed a ventral sucker, or acetabulum.Trematode Life CycleIn trematodes, one egg leads to the production of countless progeny! egg are commonly deposited in water via the to pee or feces the the critical host. When they reach freshwater, the egg opens and a ciliated free-swimming larva called a miracidium swims out. The miracidium will certainly then swim about until it find a an ideal intermediate host, which is typically an aquatic snail come which the is chemically attracted. Once the miracidium find snail, the penetrates it, loses its cilia and also develops into a sporocyst, i beg your pardon produces asexually either much more sporocysts or a number of rediae that additionally produce asexually either more rediae or tailed forms referred to as cercariae. The cercariae arise from the snail, swimming around and penetrate a 2nd intermediate host, the final (definitive) hold or encyst on vegetation (in the case of the lamb liver fluke), wherein they space transformed right into metacercariae, which space juvenile flukes; the adult grow from the metacercariae as soon as it is consumed by the definitive host.Trematode infection in HumansHumans can be infected v a variety of serious trematodes in a range of ways. In the case of the asian liver fluke (Clonorchis sinensis), infection occurs by eat raw or poorly cooked fish (which serve as the second intermediate hold of the parasite) comprise the metacercariae of the trematode.In the situation of blood flukes (Schistosoma), epidemic can take place when tailed cercariae burrow through exposed skin of human being bathing or working in waters containing the cercariae (such as eastern rice paddies). Schistosomiasis is a chronic illness that can damages internal offal and, in children, impair growth and also cognitive development. The urinary type of schistosomiasis is associated with increased risks for bladder cancer in adults, and the an illness is the 2nd most socioeconomically disastrous parasitic disease after malaria!The sheep liver fluke (Fasciola hepatica) is a usual parasite of sheep and also cattle, which come to be infected by eating aquatic tree containing encysted metacercariae (juvenile flukes). Humans can gain the parasite by eat raw watercress (which grows normally at the edges of lakes and also ponds and is cultivated in many countries in Asia and also Europe) comprise the metacercariae of the fluke.The lung fluke (Paragonimus westermani) is a potential attention parasite uncovered in Asia and South America the can cause death in human hosts. Your eggs space coughed increase from the lung of your host, swallowed and also eliminated in feces human beings can become infected by eat raw or poorly cooking freshwater crabs (the 2nd intermediate organize of the parasite) include the metacercariae the the fluke.

The class Cestoda contains about 4,000 types of tapeworms, all of which are very modified endoparasites that live in just around every known vertebrate species. The long, flattened human body of a tapeworm (which is referred to as the strobila) is split into segments referred to as proglottids. Most creates have an organ called a scolex in ~ the anterior end with suckers, hooks, etc. That affix to the wall surface of the gut and prevent them from being swept away.Tapeworms absence a digestive system and also feed by soaking up nutrients straight from the host. The whole body surface ar is covered with minute projections dubbed microtriches that substantially increase the absorptive surface area the the tapeworm. Tapeworms likewise secrete substances that inhibit the digestive enzymes of their host and lowering the pH roughly them to a level the they but not the digestive enzymes of your host have the right to function. In tapeworms, much of the strobila is provided over to reproduction. Each proglottid is monoecious, and also cross-fertilization or also self-fertilization is common. Proglottids have the right to be filled v up to 100,000 eggs!The Tapeworm Life CycleWith couple of exceptions, all cestodes call for at the very least two hosts, and also the adult is the parasite in the digestive tract of vertebrates. Often one that the intermediate master is an invertebrate (most frequently an arthropod such as a flea, louse or copepod) that is consumed by the final host. The eggs within the proglottids are melted daily in the feces right into the soil wherein they might lie dormant for quite some time. Periodically the egg-bearing proglottids crawl out of the anus by themselves and also can be discovered wriggling about on one infected dog, cat or child or ~ above infected clothing and bedding. Once the eggs are released, they have to be ingested by one intermediate organize in order to hatch right into hooked larvae referred to as oncospheres, i beg your pardon bore with the intestinal wall and choose up by the circulatory system where they room transported to skeletal muscle, love or even some other body organ where castle encyst as cysticerci (bladder worms). Every cysticercus is essentially an inside-out scolex that everts ~ the infected organization (so-called “measly meat”) of the intermediate hold is eaten by the final host. The scolex then attaches to the lining of the intestine by way of suckers and/or hooks.Tapeworm epidemic in HumansHumans can become infected with tapeworms by eating poorly cooked meat include the cysticerci that the tapeworm. The most vital tapeworms the infect people are the beef tapeworm (Taenia saginata) and also the pork tapeworm (Taenia solium).Another types of cestode that deserve to infect human beings is the broad fish tapeworm (Diphyllobothrium latum), i beg your pardon is usual in fish inhabiting the great Lakes. Again, epidemic occurs by ingesting cysticerci in life or poorly cooking fish. In most cases, tapeworms discovered in the gut do not cause much damage to their human being hosts, but occasionally they move to various other organs such together the eye or even the brain, whereby they can reason serious neurological problems and even death from cerebral cysticercosis!The dog tapeworm (Diplydium caninum) is typical in dogs however can be picked up by humans (usually kids) who ingest infected fleas that offer as intermediate hosts of the parasite.

In contrast to radiate and also acoelomate phyla in i m sorry the room between the body wall surface and the digestive street is filled with mesoglea or with solid mesenchymal parenchyma, the remaining bilateral pets covered in the Zoo laboratory website have a human body cavity in which interior organs room located. In the pseudocoelomates, the embryonic blastocoel persists together a body cavity. Since it is not lined with mesodermal peritoneum (the lining the the coelom), the is referred to as a “false cavity” or pseudocoel.

The Phylum Acanthocephala contains around 1,000 varieties of parasitic pets called spiny-headed worms, all of which are endoparasites in the intestinal tracts that vertebrates (especially fishes). Two hosts are forced to finish the life cycle, and also the juveniles are parasites that crustaceans and insects. Most varieties are quite little (less than 40 mm). Spiny-headed worms have an eversible proboscis covered with recurved spines that offers a way of attachment in the host"s intestine. Egg pass the end host and are consumed by certain insects or crustaceans wherein they hatch and also go through several developmental stages. Once the intermediate host is consumed by a bird, mammal or fish, the larva inside attaches to the intestinal wall with that is spiny proboscis.

The Phylum Rotifera contains about 1,800 species of microscopic animals called rotifers that bear an anterior crown that cilia that provide the illustration of a revolving wheel. Back cosmopolitan (widely distributed), many are found only in freshwater environments. The basic body setup of a rotifer is separated into three regions: a head, which bear a ciliated organ called a corona (wheel organ), which creates currents the draw little planktonic develops into the mouth, which opens into a muscular pharynx dubbed a mastax. The mastax is equipped with complex jaws composed of seven tough pieces dubbed trophi that are offered for grasping and chewing the prey. The trunk has the visceral organs, and also the foot (when present) is segmented and also ringed right into joints that can shorten or telescope. Pedal glands ~ above the foot secrete a difficult substance the anchors the animal to the substrate or enables it to creep in addition to leech like movements.

From this point on, all animals that will certainly be learned in the Zoo rap website are eucoelomate, that is, they have a true coelom (body cavity) that is lined through a slim layer the mesodermal tissue dubbed the peritoneum. Note: The advance of the coelom must be taken into consideration one of the most important steps in the development of larger and also more facility forms for it gives plenty of room for organs that have the right to be held in ar by slim membranes called mesenteries!

The Phylum Ectoprocta (also referred to as Bryozoa) contains around 4,000 species of tiny colonial forms dubbed moss animals that are discovered in shallow freshwater and also marine environments. Back bryozoans are also well stood for in the fossil record, they are additionally quite abundant today. Modern-day marine forms exploit all kinds of firm substrates consisting of shells, rocks, maritime timbers, and also ship bottoms. In fact, like barnacles, the ectoprocts are one of the most crucial groups the fouling biology that should be removed periodically native ship and also boat hulls. Every member the a colony lives in a small chamber referred to as a zoecium (“animal house”), which is secreted through its epidermis.Each separation, personal, instance (zooid) is composed of a feeding part and a case-forming part. The zoecium have the right to be gelatinous, chitinous or calcareous, and sometimes that is impregnated v sand grains. The feeding section of the animal contains the lophophore (a ciliated feeding maker that can additionally be offered for gas exchange), cradle tract, muscles and nervous system. Each individual lives a kind of “jack-in-the-box” existence, popping as much as feed and also then quickly withdrawing right into its security chamber that is frequently sealed through a tiny trapdoor (operculum).

The Phylum Brachiopoda (“arm foots”) contains pets that are well-known as lampshells. This is an old group the is well represented in the fossil document (with some 30,000 described species) however only about 300 living species. Brachiopods resemble bivalve molluscs, yet unlike bivalves, they have actually shells the are situated on the ventral and dorsal side rather than left and right.Brachiopods are divided into two classes based on whether they have actually shells that are associated by a hinge with interlocking “teeth” or v shells of uneven size. Brachiopods in the latter team are referred to as lampshells since the bigger ventral valve resembles a roman inn oil lamp. Part brachiopods affix themselves to the substrate through a pedicel on the ventral valve when others just cement the ventral valve to the substrate (like an oyster) or burrow into the sediment. Favor bryozoans, brachiopods also have a lophophore neighboring the mouth the is used for feeding and gas exchange.

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1. PharynxGastrovascular cavityEye spotAuricle

This slide has two specimens of the free-living turbellarian flatworm Planaria. One specimen has been stained, while the other has actually been injected through carbon black to expose the level of the blind gastrovascular cavity, i m sorry is separated into three, many-branched trunks (one anterior and also two posterior). There is no an anus, food must first pass through the mouth right into the gastrovascular cavity whereby it is digested after i m sorry waste commodities exit with the very same opening. Note the large, eversible pharynx in each planarian that is offered for feeding. In the head region are lateral projections referred to as auricles (not well emerged on the specimens shown) the contain touch and also chemical receptors and also light-sensitive ocelli (eye spots).

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Buccal cavityGastrodermisGastrovascular cavityEpidermisPharynxParenchyma

This slide contains a cross section through the pharyngeal (middle) region of the free-living flatworm Planaria. Note the big muscular pharynx that lies within a room called the buccal cavity. Throughout feeding, the pharynx have the right to be everted with the mouth and used come suck increase fluids and also soft tissue from captured prey. Two branches of the comprehensive gastrovascular cavity can additionally be seen. This cavity is lined v large, vacuolated cells that comprise the gastrodermis. ~ above the outside of the flatworm is a ciliated epidermis that consists of many gland cells and dark-staining rod-shaped bodies referred to as rhabdites that have the right to discharge their components to type a safety mucous layer around the body. Lacking a human body cavity, the room between the gut and epidermis in this acoelomates is filled with a meshwork of mesodermal parenchyma and muscle yarn that operation circularly, longitudinally and also diagonally.

Planaria c.s. (close-up)

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Gastrovascular cavityGastrodermisParenchymaRhabdites ~ above epidermis

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This slide reflects a stained totality mount of the asian liver fluke (Clonorchis sinensis), an essential trematode parasite of the humans in numerous regions of Asia, particularly China, southeast Asia and Japan. Human beings are infected by eating raw or poorly cooking fish containing the encysted metacercariae. After being ingested, this cysts dissolve in the intestine, releasing the young flukes which then migrate to the bile duct and also liver.

Anterior section

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Mouth and oral suckerPharynxEsophagusIntestinal cecumGenital poreVentral sucker (acetabulum)

Middle section

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UterusIntestinal cecaYolk glandsYolk ductOvarySeminal receptacleTestesExcretory bladder

Posterior section

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Intestinal cecaTestesExcretory bladderExcretory pore

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This slide mirrors the redia larva that a trematode parasite. This larval stage normally establishes in the tissues of an aquatic snail. The redia includes groups of cells dubbed "germ balls" the eventually develop into the tailed cercaria larvae, which emerge from the snail and also penetrate a second intermediate organize or encyst ~ above vegetation to become a metacercaria.

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This slide mirrors the tailed-cercaria larva the a trematode parasite. This larval stage, i beg your pardon normally creates in the tissue of one aquatic snail, will arise from its intermediary host and penetrate a 2nd intermediate organize or encyst on vegetation to become a metacercaria.

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ScolexImmature proglottidMature proglottidGravid proglottid

This slide contains stained sections of the dog tapeworm Diplydium caninum taken native four different regions. The anterior most portion contains the scolex, a committed attachment body organ that often consists of hooks and/or suckers. The remainder of the human body is split into a linear series of segments dubbed proglottids, every of which has a complete set of reproductive organs. The youngest proglottids in the very first part that the strobila (body) the the tapeworm are immature, when those in the middle are mature. The oldest terminal proglottids room gravid, which means they space filled with eggs. Dogs and also cats can come to be infected by eating adult fleas (the intermediary hosts) comprise cysticercoid larvae.

Scolex (close-up)

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TestesVas deferensVaginaOvaryYolk glandGenital pore

This slide reflects a mature proglottid from the dog tapeworm Diplydium caninum. Note that there room two complete sets the male and also female reproductive frameworks that incorporate testes, vasa deferentia (the plural of vas deferens), ovaries, yolk glands, vaginas and also genital pores. Dogs and cats become infected by eat adult fleas (the intermediary hosts) comprise cysticercoid larvae.

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Excretory canalTestesUterusGenital poreVas deferensVaginaOvariesYolk glands

This slide reflects a maturation proglottid indigenous the tapeworm Taenia pisiformis, a varieties commonly found in the tiny intestines that dogs and cats. Note that each segment has a complete set of reproductive structures consisting of testes, vas deferens (sperm duct), ovary, yolk gland, vagina and genital pore.

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StrobilaSuckersHooks top top rostellum

This slide mirrors a scolex native the anterior most region of the tapeworm Taenia pisiformis. Keep in mind the series of hooks on a raised part of the scolex referred to as a rostellum and the 4 lateral suckers. This hooks and also suckers enable to tapeworm to stay attached come the intestinal wall of its host.

Hooks on rostellum

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This slide mirrors a intensified view that the raised reminder of the scolex (rostellum) from the dog and also cat tapeworm Taenia pisiformis. Note the formidable selection of hooks the are used by the tapeworm to cave on to the intestinal street of that is host.

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This slide reflects the cysticercus larva that the tapeworm Taenia pisiformis. Keep in mind the invaginated scolex top top the right finish of this "bladder worm". ~ infected tissue of the intermediate host is consumed by the critical host, the scolex everts and also attaches to the lining of the intestine by method of hooks and also suckers.

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This slide mirrors a stained specimen of an adult spiny-headed worm belonging come the Phylum Acanthocephala. Although human infections have actually been recorded, adult worms typically parasitize the cradle tracts of fish, birds and domestic and wild mammals. The larvae the spiny-headed worms construct in various varieties of crustaceans or insects. Keep in mind the everted proboscis containing many recurved spines that offer the biology its name. These spines (which allow the worms to remain attached to the digestive tract) can cause massive and sometimes painful devastation of the minister mucosa.

Acanthocephalan proboscis (close-up)

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This slides shows two stained rotifers. These pseudocoelomate pets derive their name from a distinctive ciliated crown (corona) that, when beating, provides the impression that a rotating wheel. The movement of these cilia create water currents that attract food items into the mouth that the organism. Once inside, food is chewed and ground increase in a muscular part of the pharynx referred to as a mastax the is fitted with little hard jaws referred to as trophi. Back there space a few marine species, most rotifers are discovered in freshwater habitats throughout the world.

Photographs of life rotifers

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This microscope image shows two live specimens the the common rotifer Philodina. Note the lateral extension of the body wall in the head region of the specimen ~ above the right (pointed come by the red arrow). This framework (which is called an antenna) includes many, small sensory bristles. The corona ("wheel organ") include two big ciliated trochal discs and foot with its 2 toes (the spurs pointed to by the blue arrow) can be checked out on the specimen top top the left. Pedal glands (which open up by ducts in ~ the tips of the toes) create an adhesive substance supplied for short-lived attachment to the substrate.

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This microscope photo shows a intensified view that the freshwater rotifer Philodina. Keep in mind the conspicuous corona (wheel organ) with its cilia and also the centrally-located mastax (pointed come by the red arrow), a muscular portion of the pharynx equipped v chitinous jaws (trophi) the grind and also shred ingested food.

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This microscope photo shows another species of rotifer in the genus Monostyla. This usual freshwater varieties has a rigid, chitin-like covering dubbed a lorica.

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This slide shows several zooids the the freshwater ectoproct Plumatella. Keep in mind the conspicuous lophophores. This feeding tools consist the masses of ciliated tentacles borne on ridges surrounding the mouth. In enhancement to reproducing through budding, freshwater bryozoans reproduce asexually by means of distinct resistant bodies called statoblasts (not visible on this slide). These dark, disc-shaped frameworks (which are comparable to the gemmules of freshwater sponges) are developed during the summer and fall, and can stay dormant until environmental conditions improve in the spring.

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This slide reflects a part of a branching swarm of the naval bryozoan (ectoproct) Bugula. Branching in ~ the colony is developed by repetitive asexual budding the individuals called zooids. Keep in mind the tentacles the the lophophores (ciliated feeding devices surrounding the mouth that can likewise be used for gas exchange). Like many early american cnidarians, ectoproct nests are polymorphic, with many of the zooids functioning as feeding individuals. Defensive zooids dubbed avicularia defend the nest against tiny organisms, consisting of settling larvae and crawling tube-building polychaete worms and also arthropods. Every avicularium resembles the head the a bird finish with powerful musculature and also a spicy beak-like framework (rostrum) that is offered to grab the appendages the trespassing organisms.

Avicularium (close-up)

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This slide shows a magnified view of one avicularium native the marine early american bryozoan Bugula. Keep in mind the mandible, bird-like beak (which is dubbed a rostrum) and also musculature. Avicularia protect the nest from tiny organisms, consisting of settling larvae and crawling tube-building polychaete worms and arthropods.

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This is a slide of a monogenetic fluke taken native the gills of an Atlantic stingray. Unequal the digenetic trematodes, monogenetic varieties have a direct life bike in i beg your pardon ciliated larvae called oncomiracidia build on or in ~ a single host. Return a couple of species are discovered in the urinary bladders the frogs and also turtles, most such flukes cling come the gills and external surfaces of fish by method of a posterior attachment organ referred to as an opisthaptor the is equipped through hooks.

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This slide reflects a stained totality mount the the lamb liver fluke (Fasciola hepatica). This big trematode is a common parasite that sheep and cattle, which become infected by eating aquatic tree containing the encysted metacercariae (juvenile flukes). Once ingested, the cyst walls are digested and the larvae burrow v the intestinal wall surface to the body cavity and also eventually to the liver.

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This slide shows an adult specimen that the lung fluke Paragonimus westermani. Uncovered in east Asia, southwest Pacific and also some components of southern America, the fluke parasitizes a variety of wild carnivores, pigs, rodents and humans. Infection through lung flukes reasons respiratory symptoms, v breathing difficulties and also chronic cough, and also fatalities are common! Humans obtain infected through lung flukes by eat raw or poorly-cooked freshwater crabs comprise the fluke metacercariae.

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This slide mirrors a pair that adult blood flukes in copulation. Blood flukes differ from many other flukes by gift dioecious (i.e., having separate sexes). Males space larger and also have a large, ventral groove called a gynecophoric canal posterior to the ventral sucker that holds the smaller sized (more darkly stained) female throughout copulation, i beg your pardon is continuous. Schistosoma mansoni is just one of the three species of blood flukes responsible because that the disease in humans referred to as schistosomiasis. Humans acquire infected as soon as the tailed cercaria larvae (which escape native freshwater snails that offer as their intermediate hosts) burrow right into the exposed skin of individuals bathing, swimming or functioning in such habitats.

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This model has several see of a free-living turbellarian flatworm. The picture on the left shows the nervous mechanism (painted white), which consists of a pair of cerebral ganglia through two ventral nerve cords that are connected by a series of transverse nerves referred to as commissures, giving it a ladder-like appearance. Various other sensory structures encompass simple, light-sensitive eyes (ocelli) and chemical receptors the are concentrated in lateral projections that the head dubbed auricles (because they look choose ear lobes). Back reproduction in planarians can occur asexually v fission, all forms are monoecious v both male and also female reproductive organs. Several attributes of the reproductive mechanism (shown in blue and also yellow) are also seen on the design on the left. The design on the right shows the plenty of branched gastrovascular cavity (shown in red) that exits through a single ventral opened at the end of a muscular, eversible pharynx (shown in off-white top top both models as well as on the small upper planarianmodel). Additionally seen top top the version is a section of the excretory/osmoregulatory system (shown in green) that is made up of protonephridia that collect and also secrete some wastes as well as the overfill water the enters freshwater creates by osmosis. Protonephridia consists excretory tubules that room closed internally and also open come the external by a series of collecting ducts that bring about a posterior opening referred to as a nephridiopore. The internal ends of every of these tubules end in so-called flame cell (one of which is shown on the small, lower model), which have actually tufts that cilia the flicker choose the flame of a candle. The beating of these cilia traction water through a mesh-like cup, creating a filtrate that water and little molecules.

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Anterior sections

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Cerebral ganglionVentral nerve cordOcellusAuriclesTestesOvaryOviductCircular muscle layerLongitudinal muscle layer

Posterior sections

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Gastrovascular cavityPharynxExcretory systemVentral nerve cordTestesSeminal vesicleOviductParenchyma

Flame cabinet close-up

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CiliaCollecting ductFlame cell nucleusParenchyma

33. Oriental liver fluke (Clonorchis sinensis) model

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This picture shows a model of the oriental liver fluke (Clonorchis sinensis), critical trematode parasite of the people in numerous regions the Asia. People are infected by eat raw or under cooked fish include the encysted metacercariae. After being ingested, these cysts dissolve in the intestine, releasing the young flukes i m sorry then migrate to the bile duct and also liver. For close-up views of labeled structures found in different sections that the liver fluke, click the links below.


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1. Pharynx; 2. Cerebral ganglia; 3. Minister ceca; 4. Seminal vesicle; 5. Uterus


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1. Mouth; 2. Oral sucker; 3. Esophagus; 4. Intestinal ceca; 5. Ventral sucker;6. Genital pore; 7. Uterus; 8. Yolk glands


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1. Seminal vesicle; 2. Uterus; 3. Minister cecum; 4. Seminal receptacle;5. Excretory bladder; 6. Excretory pore; 7. Yolk ducts; 8. Mehlis" gland


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1. Uterus; 2. Yolk glands; 3. Mehlis" gland; 4. Ovary; 5. Seminal receptacle; 6. Testes; 7. Excretory bladder; 8. Minister cecum