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Phylum Platyhelminthes
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I. Characteristics of Flatworms
A. Three germ layers make them triploblastic 1. Ectoderm – outer layer 2. Mesoderm – middle layer, containing organs 3. Endoderm – inner layer, lines digestive cavity. B. Bilateral Symmetry – with true cephalization in the form of cerebral ganglia. C. Body flattened dorsoventrally, openings underneath D. Outer tegument for parasitic forms ONLY E. Primitive muscular system arising from Mesoderm F. Acoelomate – No true body cavity; no organs inside
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G. Incomplete digestive system – gastrovascular cavity
H. Ladder Type Nervous System I. Simple sense organs – free living ones have Ocelli J. Simple excretory system – some with flame cells K. NO respiratory, circulatory or skeletal systems. L. Most forms are monoecious (hermaphrodites)
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II. Classification of Flatworms
A. Class Turbellaria 1. Mostly free living 2. Most well known is the Planarian 3. Digestive system has a mouth, pharynx, and intestine which together forms a gastrovascular cavity. 4. Ocelli are common in Planaria. 5. Asexual Reproduction occurs by fission. 6. Sexual reproduction is by cross fertilization; Planaria are hermaphrodites, but cannot fertilize themselves. 7. They have remarkable regenerative capabilities.
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Typical Planarian Ocelli
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B. Class Trematoda – parasitic flukes
1. Outer body covered by protective tegument 2. Two hosts in some life cycles intermediate – contain larvae definitive – contain sexual adults
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Chlonorchis sinensis (Southeast Asia)
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Chlonorchis sinensis – human liver fluke
a. eggs are deposited in water sources through human feces. b. eggs are ingested by the FIRST intermediate host – the snail. (Parafossarulus) c. The larvae hatch from the eggs and live in the snail until they develop into cercariae. d. The cercariae dig out of the snails and swim around. They burrow into a certain family of fishes, (Cyprinidae) which are their SECOND intermediate host. e. Humans catch and eat the fish. f. The cercariae become adult worms in the definitive host and attack the liver and intestines, where they may live 15 – 30 years.
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Schistosoma spp. Asia Africa Central and South America
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Schistosoma – Human Blood Flukes (several species)
a. Eggs are deposited into the water through human feces. b. The eggs hatch and larvae penetrate snails in the water. c. The larvae dig their way out of the snails. d. The free swimming larvae, known as cercariae, search for humans in the water – bathing, washing clothes, swimming, fishing, etc. e. They penetrate the humans and bore into circulatory and intestinal systems. f. They cause a disease known as schistosomiasis.
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Beef Tapeworm Means “pregnant”
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C. Class Cestoda – The Tapeworms
1. The head or holdfast of a tapeworm is called the scolex. 2. The individual reproductive segments are proglottids. 3. The entire chain of proglottids is called the strobila. 4. Taenia saginata – The Beef Tapeworm a. intermediate host – cow b. definitive host – humans 5. Taenia solium – The Pork Tapeworm a. intermediate host – pig b. definitive host - humans
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Phylum Nematoda The Roundworms
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I. Characteristics of Roundworms
A. Pseudocoelomates - no true body cavity; organs inside not attached to cavity walls B. Hydrostatic Pressure for shape and structure. C. Most roundworms are less than 5 cm long, but some are over one meter in length. D. Outer protective cuticle made primarily of collagen. E. MOST nematodes are dioecious. F. Roundworms lack circulatory and respiratory systems, just as flatworms do.
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The flatworms showed us an acoelomatic arrangement.
The Roundworms show us a pseudocoelomatic arrangement.
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Flatworm arrangement
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Roundworm Arrangement
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II. Classification of Roundworms
Ascaris 1. Most well known roundworms; easily studied 2. Infection comes from eating undercooked vegetables 3. Infects intestines; eggs pass through fecal matter.
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Mississippi leads the nation in Hookworm infestation!
B. Hookworms 1. Enter body through skin of feet 2. Eggs pass out through fecal matter 3. Heavy infestations cause anemia Mississippi leads the nation in Hookworm infestation! Don’t go barefoot!
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1. Trichina worm found in pig skeletal muscle.
C. Trichinella 1. Trichina worm found in pig skeletal muscle. 2. Contracted by eating undercooked pork. 3. Causes a disease called trichinosis. Typical Trichina larva inside pork – cook it well!
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D. Filarial Worms – carried by insects (usually flies and mosquitoes!)
Heart Worms – Attack dogs, cats, even humans, get into heart and clog it up, preventing free blood flow – often fatal for small animals
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2. Wuchereria bancrofti – filarial worm obtained from mosquito bites
2. Wuchereria bancrofti – filarial worm obtained from mosquito bites. They block the flow of the lymph nodes and lymphatic fluid. They cause a disease known as Elephantiasis.
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Elephantiasis is marked by excessive growth and swelling, especially in the scrotum, legs, arms, and on occasion the vulva and breasts of human hosts.
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Discussion Question for this Unit!!!***
Pinworms are usually ingested by children or adults after getting them on their hands from the soil. The eggs are often found under the fingernails of the person involved. The hands are then placed in the mouth, causing the eggs to hatch.
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The larvae migrate to the intestines, where
the male and female worms reproduce. The female crawls out of the host’s anus at night, laying her eggs around the anal sphincter with a glue-like substance that itches tremendously.
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To prevent, wash hands and keep fingers out of mouth!
The host then scratches the anal area at night, causing the eggs to end up back under the fingernails. After placing their hands in their mouths, the process starts all over again! To prevent, wash hands and keep fingers out of mouth! 30% of all toddlers in the USA get pinworms ! 16% of all adults in the USA get pinworms ! This is the most common helminth parasite in America!
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That's all Folks! TEST NEXT CLASS PERIOD!
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