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Unit 5.1 Phylum Platyhelminthes 1 Phylum Platyhelminthes • Flat worms • Triploblastic – three primary germ layers • Acoelomate – no body cavity • Bilateral symmetry • Hermaphroditic – Monoecious – Having both sperm and egg producing parts • One opening for digestive system – located ventrally. Food is eaten and excreted through the same tube. 2 Phylum Platyhelminthes • Paired lateral nerve cords & cerebral ganglion – very simple • Flame cells – specialized “kidney” cells • No specialized circulatory or respiratory systems – must be flat so nutrients & oxygen can diffuse throughout the body 3 Uniramia Echinodermata Chordata Lophophorates Chelicerata Crustacea Protochordates Arthropoda Annelida Hemichordata Other pseudocoelomates Nematoda Mesozoa Sarcomastigophora Ciliophora Apicomplexa Microspora Mollusca Nemertea Platyhelminthes Ctenophora Cnidaria Placozoa Porifera Myxozoa 4 Acoelomate Ectoderm Mesoderm Endoderm Coelom – A fluid filled space that is completely surrounded by mesoderm 5 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Platyhelminthes: Class Turbellaria Acoelomate 7 Pseudocoelomate Ectoderm Mesoderm Endoderm Coelom – A fluid filled space that is completely surrounded by mesoderm 8 Coelomate Ectoderm Mesoderm Endoderm Coelom – A fluid filled space that is completely surrounded by mesoderm 9 Nervous System Lateral nerve cord Cerebral ganglion Connectives Eye spot Auricle 10 Brain Auricle Cerebral ganglion Paired nerve cords 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Excretory System 12 13 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Turbellaria 15 16 Class Turbellaria • Eye spots – detect simple light gradients. • Ciliated skin surface secretes mucous and aids in movement. • May be aquatic or terrestrial. Terrestrial species are all nocturnal. • Most are free-living – not parasites but predators/scavengers. 17 Class Turbellaria • Planarians have the ability to regenerate new body parts or to generate an entirely new organism from pieces of themselves. 18 19 Class Trematoda • Flukes • Parasites • Holdfast devices – Most possess these • Complex life cycle • Intermediate host – Animal with juvenile stage • Definitive host – Animal with adult stage 20 21 Clonorchis sinensis Oral sucker Intestine Uterus Yolk gland Ovary Seminal recepticle Testes 22 23 Clonorchis sinensis • Chinese liver fluke • 50 million people infected. • Cirrhosis of liver – liver tissue is replaced by nonfunctioning scar tissue that impairs overall liver function • Diarrhea • Edema – fluid beneath the skin. • Severe gut pain. 24 25 Fascioloa hepatica • Sheep liver fluke • Sheep, cattle and man – Weight loss • Eat vegetation contaminated with metacercariae – small capsules that house the intermediate stage of the fluke. 26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life Cycle of the Sheep Liver Fluke 27 Fasciolopsis buski • • • • Intestinal fluke 10 million people Man and pigs Hemorrhage and abscesses of small intestine 28 29 Paragonimus westermani • Lung fluke • Carnivores, pigs, rodents and man • May be fatal 30 31 32 Schistosoma • Blood flukes – parasitize mesenteric blood vessels. • 200 million people infected. • 1 million deaths/year. • Second most deadly parasite behind malaria. • Males wrap around females & they exist in pairs throughout adult lives. 33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life Cycle of a Schistosome Fluke Eggs are expelled in urine or feces to fresh water where the larvae pass through an intermediate stage involving a snail host and then enter through the skin of a passing human host. 34 Schistosoma • The eggs all have a hook that tears bodily tissues throughout the human host causing more damage as they are passed. • Larvae have a forked tail that assist them in borrowing through human skin. 35 Schistosoma 36 Swimmers Itch – Related to Blood Fluke 37 Swimmers Itch • Need avian hosts to complete their life cycle. • Humans are “accidentally” infected and develop a rash for around a week. • Sores develop around burrowing sites but the larvae die within a few hours of entering the skin 38 Class Cestoidea • Tapeworms • No digestive system – suck in pre-digested nutrients from the intestines of the host that are directly utilized in metabolic processes. • Can grow up to 100 feet long. Human tapeworms may reach 60 feet in length. 39 Class Cestoidea • The scolex, or head, is equipped with suckers designed to anchor the worm to the intestinal wall and to suck in nutrients. • The proglottids are hermaphroditic segments, each able to detach from the body and produce eggs. 40 Class Cestoidea • Infections are usually asymptomatic other than lethargy and/or dull abdominal pain. • The lethargy is due to a lack of nutrients caused by the tapeworms’ feeding. This leads to weight loss. • People may purposefully infect themselves with tapeworms to lose weight. 41 Scolex 42 Proglottid Testes Uterus Vas deferens Seminal receptacle Ovary Yolk gland 43 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pork Tapeworm (Taenia solium) 44 Taenia saginata 45 Echinococcus granulosus • A tapeworm that causes a potentially fatal parasitic disease called hydatid disease. • Herbivores, and sometimes humans, become the intermediate hosts after ingesting eggs on vegetation. 46 Echinococcus granulosus • The eggs then hatch into embryos that lodge in tissues and grow into huge cysts containing thousands of tapeworm larvae. • When the cysts finally cause the host to die or become easy prey, they are ingested by the scavenger/predator and become adults in their intestinal tracts. 47 48 The End 49