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PHYLUM PLATYHELMINTHES. “Means flatworm”. Characteristics. There are about 20,000 species and more than 85% are parasitic. Flatworms live in marine , freshwater and moist terrestrial environments . They are triploblastic , which means they have three germ layers
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PHYLUM PLATYHELMINTHES “Means flatworm”
Characteristics • There are about 20,000 species and more than 85% are parasitic. • Flatworms live in marine, freshwater and moist terrestrial environments. • They are triploblastic, which means they have three germ layers ( endoderm, mesoderm, and ectoderm)
4.They are the most primitive animals to have bilateral symmetry and minimal cephalization, where the sense organs become localized in the anterior end of the animal. 5. They have no coelom ( body cavity) so they are considered to be an acoelomate. They have a digestive tube with the space between the ectoderm and the endoderm filled with a fibrous cellular packing material called parenchyma. 6. Because they show more specialization and division of labor they have reached the organ system level of development
7. Digestive system is incomplete because there is only one opening; one class, Cestoda ( the tapeworms) have no digestive system. 8. Excretory system of two lateral canals with flame cells 9. No circulatory or Gas exchange systems 10. They have some simple sense organs such as eyespots (ocelli) in some and chemoreceptors in most flatworms, especially the auricles of planarians. Some have statocysts for gravity and some have rheotaxisfor water current direction. 11. Most forms are monoecious, usually with well-developed gonads and internal fertilization. Some have directdevelopment,where the juvenile form appears to be a smaller version of the adult. Some have indirect development with complicated life cycles involving several hosts
12. Nervous system with 1-5 pairs of longitudinal nerve cords and a ganglion to form the beginnings of a brain 13. Skeleton is hydrostatic There are four diverse classes of flatworms 1. class Turbellariameans “ commotion-like” 2. class Trematoda means “ perforated form”
3. class Monogenameans “ single kind” 4. class Cestoda means “ girdle form”
Characteristics of Turbellaria • A. most are free living and non-parasitic • B. Range in size from 5mm to 50cm • C. Locomotion by cilia or glide on a slime trail
D. most well know species of this class is Planariawhich are extensively used in the laboratory 1. Planaria are mainly carnivorous and feed mostly on small crustaceans and insects. They wrap their body around prey and evert a pharnyxthrough the mouth located on the ventral side of the body, to suck up their prey. 2. Planaria have considerable powers of regeneration Ex. A piece of planaria cut from the middle of the body will grow both a new head and a new tail 3. Planaria are freshwater and some are found in moist soil usually living under rocks or rotting logs in tropical rain forests.
Characteristics of class Trematoda ( flukes) • There are about 11,000 species • All trematodes are endoparasitic • Most adult trematodes are digestive trac parasites of vertebrates • Have structural adaptations for parasitism • Penetration glands or glands to produce cyst material • Organ for adhesions such at hooks and suckers • Increased reproductive capacity • E. sense organs are poorly developed or absent
Sub class Digenameans “ double race” Have indirect life cycle with first intermediate host being a mollusc ( usually a snail) B. The definitive or final host is always a vertebrate
C. General life cycle of Trematodes (flukes) The egg passes in feces and must reach the water Egg hatches into a free swimming Miracidium Miricidium finds a snail and penetrates the tissue to form a sporocyst Inside the snail, the sporocyst produces many rediaeasexually the many rediae produce many more cercariaewith tails, asexually Cercariae emerge from the snail and either penetrate a second intermediate host or encyst on vegetation to become metacercariae, which are juvenile flukes The adult grows from a metacercariae when that stage is eaten by the right definitive host
Sheep liver fluke (Faciola hepatica) Adult fluke lives in the liver of sheep and the eggs are passed In the feces of the sheep. After two generations inside snails, the Cercariae emerge to encyst on vegetation and wait to be eaten by other sheep.
Human Liver Fluke (clonorchissinensis) Common in E. Asia, especially in China, Japan, and S.E. Asia. Other animals that are also infected by this fluke are Cats, Dogs, and Pigs. Vary in length from 10mm to 30mm. Usually found in bile passageways of humans and other fish eating mammals. Eggs are shed into water with feces but do not hatch until they are eaten by certain snails.Cercariae escape into the water and swim until they find one certain kind of fish and bore into its muscle,encyst as Metacercariae. When ever a mammal eats raw infected fish, the metacercarial cyst dissolves in the intestine and the young fluke migrates up the bile duct. There they become adults and may live for 15-30 years. A heavy infestation of liver flukes can destroy the liver and result in death. This can be controlled by destroying snails and thoroughly cooking all fish.
Human Blood Flukes(Schistosoma) Causes a disease called Schistosomiasis which infects over 200 million people and is very common in Africa, So. America and the middle and far east. Eggs hatch from feces, in water, and form a miricidium( ciliated larvae) that penetrate a certain species of snail. After two generations in the snail, they form Cercaria which swim in water until they contact bare human skin. They pierce the skin and shed their tails, swim up blood vessels to the liver where they develop and then migrate to the appropriate blood vessel, the large intestine, the small intestine, or the bladder causing abscesses, bloody diarhea, ulcers and abdominal pain.
Swimmers itch: (Schistosome dermatitis) Various species of schistosomes can penetrate the skin of humans and cause intense itching and a rash. These schistosomes do no real harm because humans are not the definitive host. Many northern American lakes are heavily infested.
III. Characteristics of class Monogena • Monogeans are all ectoparasites, primarily of frogs and the gills of fish • Have a direct life cycle in a single host • The oncomiracidium ( ciliated larvae) attaches to a host’s gills with posterior hooks which become the attachment organ of the adult is called the opisthapor. • These parasites can become serious pests of fish farming
IV. Characteristics of class Cestoda A. They have a flattened and segmented body. B. Each segment is called a proglottidand contains a set of reproductive organs. A chain of proglottids is called a strobila.Proglottids originate in an area called the germanitive zone which is behind the head.
C. Nearly all tapeworms are monoecious • D. They have no digestive track, living off the intestinal contents of the host which they digest through the epidermis. • They have no stomach or intestine • Have a specialized structure called • the scolex, or holdfast, which is • located on the head portion • and is the organ of attachment. • It is formed with hooks and • suckers for attachment to the • intestinal wall. • G. Almost all cestodes require two • hosts, the adult lives in the • intestine of the definitive host • H. There are almost 1000 species of • tapeworm known, infecting almost • All types of vertebrates
Beef tapeworm (Taeniasaginata) This tapeworm is found as an adult in the intestine of humans. The juvenile form is found in muscle tissue of cattle. Mature adults can reach over 30 ft. in length with over 200proglottids. The scolex has four suckers for attachment. Gravid proglottidsare passed in fecal material and crawl out and dry and rupture. Embryos are viable on grass for five months and are picked up by cattle grazing. Infected people can expel many proglottids daily. Humans become infected by eating rare cooked roast beef, steaks and barbecue.
Pork tapeworm (Taeniasolium) • This tapeworm lives in the small intestine of humans and the juvenile form is found in the muscles of pigs. The life cycle is the same as the beef tapeworm except humans become infected by eating improperly cooked pork. This infection is much more dangerous because if the proglottids or eggs are accidentally ingestee, the liberated embryos called Cystcercican develop and migrate to several organs in the human body. This condition is called Cysteriosis. Common sites of infection are the eyes and the brain, which results in blindness or death.
Fish tapeworm (diphyllobothriumlatum) This tapeworm is found in the intestine of humans , dogs, cats, and other mammals. Immature stages are in crustaceans and fish. This is the longest tapeworm to infect humans with a length of over 65 ft. this tapeworm can cause a serious anemia. Fish tapworm infections can occur anywhere in the world where people commonly eat raw fish. In the United States infections, are most common in the great lakes region.
