14-1 CHAPTER 14 Flat Worms: Phylum Platyhelminthes Flat Worms: Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display General Features General Features Animals that actively seek food, shelter, home sites, and mates require a different set of strategies and body organization than radially symmetrical sessile organisms Animals that actively seek food, shelter, home sites, and mates require a different set of strategies and body organization than radially symmetrical sessile organisms Two major evolutionary advances in phylum Two major evolutionary advances in phylum Cephalization Cephalization Concentrating sense organs in the head region Concentrating sense organs in the head region Bilateral symmetry Bilateral symmetry Body can be divided along only 1 plane of symmetry to yield 2 mirror images of each other Body can be divided along only 1 plane of symmetry to yield 2 mirror images of each other First phylum with Right and Left sides First phylum with Right and Left sides

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display General Features Acoelomates Acoelomates Typical acoelomates have only one internal space, the digestive cavity Typical acoelomates have only one internal space, the digestive cavity Without coelom (additional body cavity) Without coelom (additional body cavity) Triploblastic Triploblastic Endoderm, Ectoderm, and Mesoderm Endoderm, Ectoderm, and Mesoderm 1st phyla to have 3 germ layers 1st phyla to have 3 germ layers Protostomes Protostomes blastopore becomes the mouth blastopore becomes the mouth Incomplete Gut Incomplete Gut One opening One opening

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Phylum Platyhelminthes Characteristics Commonly called flatworms Commonly called flatworms Vary from a millimeter to many meters in length Vary from a millimeter to many meters in length Some free-living; others parasitic Some free-living; others parasitic

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Platyhelminthes is divided into three classes: Turbellaria (Planaria), Trematoda (flukes), and Cestoda (tapeworm) Platyhelminthes is divided into three classes: Turbellaria (Planaria), Trematoda (flukes), and Cestoda (tapeworm) All members of Trematoda (flukes) and Cestoda (tapeworms) are parasitic All members of Trematoda (flukes) and Cestoda (tapeworms) are parasitic Class Turbellaria Class Turbellaria Mostly free-living forms Mostly free-living forms Most are bottom dwellers in marine or freshwater Most are bottom dwellers in marine or freshwater Freshwater planarians Freshwater planarians Found in streams, pools, and hot springs Found in streams, pools, and hot springs Terrestrial flatworms limited to moist places Terrestrial flatworms limited to moist places Phylum Platyhelminthes

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Form and Function Epidermis and Muscles Epidermis and Muscles Most have cellular, ciliated epidermis on a basement membrane Most have cellular, ciliated epidermis on a basement membrane Most turbellarians have dual-gland adhesive organs Most turbellarians have dual-gland adhesive organs Viscid gland cells fasten microvilli of anchor cells to substrate Viscid gland cells fasten microvilli of anchor cells to substrate Secretions of gland cells provide a quick chemical detachment Secretions of gland cells provide a quick chemical detachment Phylum Platyhelminthes

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nutrition and Digestion Some have a mouth, pharynx, and intestine Some have a mouth, pharynx, and intestine In planarians In planarians Pharynx may extend through the ventral mouth Pharynx may extend through the ventral mouth Intestine has three branches Intestine has three branches One anterior and two posterior One anterior and two posterior Mouth of trematodes (parasitic flukes) Mouth of trematodes (parasitic flukes) Opens near the anterior end Opens near the anterior end Pharynx is not extensible Pharynx is not extensible Intestine ends blindly, varies in degree of branching Intestine ends blindly, varies in degree of branching Phylum Platyhelminthes

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Planaria (Turbellaria) Planaria (Turbellaria) Carnivorous and detect food by chemoreceptors Carnivorous and detect food by chemoreceptors Food trapped in mucous secretions from glands Food trapped in mucous secretions from glands Wrap themselves around prey Wrap themselves around prey Extend the pharynx to suck up bits of food Extend the pharynx to suck up bits of food Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Trematodes (parasitic flukes) Trematodes (parasitic flukes) Feed on host cells, cellular debris, and body fluids Feed on host cells, cellular debris, and body fluids Enzymes from the intestine are secreted for extracellular digestion Enzymes from the intestine are secreted for extracellular digestion Phagocytic cells in gastrodermis complete digestion at intracellular level Phagocytic cells in gastrodermis complete digestion at intracellular level Undigested food egested out the pharynx Undigested food egested out the pharynx Cestodes (tapeworm) Cestodes (tapeworm) Rely on the host’s digestive tract Rely on the host’s digestive tract Absorb digested nutrients Absorb digested nutrients Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Excretion and Osmoregulation Flatworms have protonephridia (kidney) Flatworms have protonephridia (kidney) Used for osmoregulation Used for osmoregulation Beating flagella drive fluids down collecting ducts Beating flagella drive fluids down collecting ducts Wall of the duct beyond the flame cell bears folds or microvilli to resorb ions and molecules Wall of the duct beyond the flame cell bears folds or microvilli to resorb ions and molecules Majority of metabolic wastes Majority of metabolic wastes Removed by diffusion through body wall Removed by diffusion through body wall Collecting ducts join and empty at nephridiopores Collecting ducts join and empty at nephridiopores Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nervous System Subepidermal nerve plexus resembles nerve net of cnidarians Subepidermal nerve plexus resembles nerve net of cnidarians One to five pairs of longitudinal nerve cords lie under the muscle layer One to five pairs of longitudinal nerve cords lie under the muscle layer Freshwater planarians Freshwater planarians Brain is a bilobed cerebral ganglion (mass of nerve cells) anterior to the ventral nerve cords Brain is a bilobed cerebral ganglion (mass of nerve cells) anterior to the ventral nerve cords Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sense Organs Ocelli (light-sensitive eyespots) Ocelli (light-sensitive eyespots) Present in turbellarians, and larval trematodes Present in turbellarians, and larval trematodes Tactile and chemoreceptive cells Tactile and chemoreceptive cells Abundant Abundant Statocysts (equilibrium) and rheoreceptors (sense direction of water currents) Statocysts (equilibrium) and rheoreceptors (sense direction of water currents) Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Reproduction and Regeneration Fission Fission Many turbellarians constrict behind the pharynx and separate into two animals Many turbellarians constrict behind the pharynx and separate into two animals Each half regenerates the missing parts Each half regenerates the missing parts Provides for rapid population growth Provides for rapid population growth Regeneration Regeneration If the head and tail are cut off If the head and tail are cut off Each end grows the missing part; it retains polarity Each end grows the missing part; it retains polarity Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nearly all are monoecious (hermaphroditic) but cross-fertilize Nearly all are monoecious (hermaphroditic) but cross-fertilize Male Structures Male Structures One or more testes are connected to one vas deferens One or more testes are connected to one vas deferens The vas deferens runs to a seminal vesicle The vas deferens runs to a seminal vesicle A nipple-like penis or extensible tentacle is the copulatory organ A nipple-like penis or extensible tentacle is the copulatory organ Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Turbellarians develop male and female organs opening at a common pore Turbellarians develop male and female organs opening at a common pore After copulation, eggs and yolk cells enclosed in small cocoon After copulation, eggs and yolk cells enclosed in small cocoon Attach by a stalk to plants Attach by a stalk to plants Embryos emerge and resemble little adults Embryos emerge and resemble little adults Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Classification of Phylum Platyhelminthes Class Turbellaria - planaria Class Turbellaria - planaria Class Trematoda - flukes Class Trematoda - flukes Class Cestoda - tapeworm Class Cestoda - tapeworm Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Class Turbellaria Mostly free-living Mostly free-living Range from 5 mm to 50 cm long Range from 5 mm to 50 cm long Very small planaria swim by cilia Very small planaria swim by cilia Others move by cilia Others move by cilia Glide over a slime track secreted by adhesive glands Glide over a slime track secreted by adhesive glands Rhythmical muscular waves pass backward from the head Rhythmical muscular waves pass backward from the head Phylum Platyhelminthes

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Classification of Phylum Platyhelminthes Class Turbellaria - planaria Class Turbellaria - planaria Class Trematoda - flukes Class Trematoda - flukes Class Cestoda - tapeworm Class Cestoda - tapeworm Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Class Trematoda All trematodes are parasitic flukes All trematodes are parasitic flukes Most adults are endoparasites (inside) of vertebrates Most adults are endoparasites (inside) of vertebrates They resemble turbellaria but the tegument (skin) lacks cilia in adults They resemble turbellaria but the tegument (skin) lacks cilia in adults Sense organs are poorly developed Sense organs are poorly developed Adaptations for parasitism include: Adaptations for parasitism include: Penetration glands Penetration glands Hooks and suckers for adhesion Hooks and suckers for adhesion Increased reproductive capacity Increased reproductive capacity Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display General Trematoda Life Cycle General Trematoda Life Cycle Egg passes from definitive host and must reach water Egg passes from definitive host and must reach water Hatches into a free-swimming ciliated larva, the miracidium Hatches into a free-swimming ciliated larva, the miracidium Miracidium penetrates tissues of a snail Miracidium penetrates tissues of a snail Transforms into a sporocyst Transforms into a sporocyst Sporocyst reproduces asexually to form redia Sporocyst reproduces asexually to form redia Rediae reproduce asexually and form cercaria Rediae reproduce asexually and form cercaria Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cercariae emerge from the snail Cercariae emerge from the snail Penetrate a 2 nd intermediate host (fish) Penetrate a 2 nd intermediate host (fish) Develop into metacercariae (juvenile flukes) Develop into metacercariae (juvenile flukes) Metacercaria develop into adults when eaten by definitive host Metacercaria develop into adults when eaten by definitive host Some serious parasites of humans and domestic animals are trematodes Some serious parasites of humans and domestic animals are trematodes Example: sheep live fluke, human liver fluke Example: sheep live fluke, human liver fluke Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sheep Liver Fluke ( Fasciola hepatica) Adult fluke lives in bile passageways in the liver of sheep Adult fluke lives in bile passageways in the liver of sheep Eggs are passed out in feces Eggs are passed out in feces Miracidia hatch and penetrate snails to become sporocysts Miracidia hatch and penetrate snails to become sporocysts After two generations of rediae After two generations of rediae Cercaria encyst on vegetation and await being eaten by sheep Cercaria encyst on vegetation and await being eaten by sheep When eaten, metacercariae develop into young flukes When eaten, metacercariae develop into young flukes Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Clonorchis sinensis: Human Liver Fluke Most important human liver fluke Most important human liver fluke Common in China, Japan, and Southeast Asia Common in China, Japan, and Southeast Asia Also infects cats, dogs, and pigs Also infects cats, dogs, and pigs Adult fluke is 10–20 mm long with an oral and ventral sucker Adult fluke is 10–20 mm long with an oral and ventral sucker Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Clonorchis Life Cycle (Liver Fluke) Adults live in bile passageways of humans and other fish-eating mammals (sexual reproduction occurs here) Adults live in bile passageways of humans and other fish-eating mammals (sexual reproduction occurs here) Eggs containing a complete miracidium are shed into water with feces Eggs containing a complete miracidium are shed into water with feces The eggs hatch only when ingested by snails of specific genera The eggs hatch only when ingested by snails of specific genera Miracidium enters snail tissue and transforms into a sporocyst Miracidium enters snail tissue and transforms into a sporocyst Sporocyst produces one generation of rediae, which begin differentiation (asexual reproduction) Sporocyst produces one generation of rediae, which begin differentiation (asexual reproduction) Phylum Platyhelminthes

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Rediae pass into the snail liver Rediae pass into the snail liver Turns into tadpole-like cercariae Turns into tadpole-like cercariae Cercariae escape into water Cercariae escape into water Make contact with fish Make contact with fish Bore into fish muscles or under scales Bore into fish muscles or under scales Shed tail and turn into a metacercariae cyst Shed tail and turn into a metacercariae cyst A mammal eats raw fish A mammal eats raw fish Cyst dissolves and flukes migrate up bile duct Cyst dissolves and flukes migrate up bile duct Heavy infection can destroy the liver and result in death Heavy infection can destroy the liver and result in death Control of parasites Control of parasites Destroy snails and thoroughly cook fish Destroy snails and thoroughly cook fish Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Schistosoma: Blood Flukes Over 200 million people infested with schistosomiasis Over 200 million people infested with schistosomiasis Common in Africa, South America, West Indies, and the Middle and Far East Common in Africa, South America, West Indies, and the Middle and Far East Sexes are separate Sexes are separate 3 species with varied location: 3 species with varied location: large intestine large intestine small intestine small intestine urinary bladder urinary bladder Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Schistosoma Life Cycle Eggs discharged in human feces or urine Eggs discharged in human feces or urine In water, eggs hatch as ciliated miracidia In water, eggs hatch as ciliated miracidia Contact with a particular species of snail to survive Contact with a particular species of snail to survive In the snail, they transform to sporocysts In the snail, they transform to sporocysts Sporocysts produce cercaria directly Sporocysts produce cercaria directly Cercariae escape the snail and swim until they contact bare human skin or other host Cercariae escape the snail and swim until they contact bare human skin or other host Cercariae pierce the skin and shed their tails Cercariae pierce the skin and shed their tails Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Enter blood vessels and migrate to the hepatic portal blood vessels (blood vessel from digestive tract to liver) Enter blood vessels and migrate to the hepatic portal blood vessels (blood vessel from digestive tract to liver) Develop in the liver and they migrate to target sites Develop in the liver and they migrate to target sites Eggs released by females are extruded through gut or bladder lining and exit with feces or urine Eggs released by females are extruded through gut or bladder lining and exit with feces or urine Eggs that remain behind become centers of inflammation Eggs that remain behind become centers of inflammation Phylum Platyhelminthes

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cut Liver of individual who dies from hematemesis (vomiting blood). 180 adult flukes were found in autopsy

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Control: proper disposal of human wastes Control: proper disposal of human wastes Schistosoma dermatitis (swimmer’s itch) Schistosoma dermatitis (swimmer’s itch) Occurs when cercariae penetrate an unsuitable host such as a human (our immune system fights them off leading to inflammation -itch) Occurs when cercariae penetrate an unsuitable host such as a human (our immune system fights them off leading to inflammation -itch) Normal host many be a bird or other animal Normal host many be a bird or other animal Phylum Platyhelminthes

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Classification of Phylum Platyhelminthes Class Turbellaria - planaria Class Turbellaria - planaria Class Trematoda - flukes Class Trematoda - flukes Class Cestoda - tapeworm Class Cestoda - tapeworm Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Class Cestoda Tapeworms have long flat bodies with scolex Tapeworms have long flat bodies with scolex Holdfast structure with suckers and hooks Holdfast structure with suckers and hooks Scolex is followed by a linear series of reproductive units or proglottids Scolex is followed by a linear series of reproductive units or proglottids Lack a digestive system Lack a digestive system Lack sensory organs except for modified cilia Lack sensory organs except for modified cilia Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Tapeworm: Scolex is site of attachment.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Tegument of a Tapeworm: Many microthriches help increase surface area for absorption.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Tegument is has no cilia Tegument is has no cilia Entire surface of cestodes is covered with projections (microtriches) similar to microvilli seen in the vertebrate small intestine Entire surface of cestodes is covered with projections (microtriches) similar to microvilli seen in the vertebrate small intestine Microtriches increase the surface area for food absorption Microtriches increase the surface area for food absorption Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nearly all cestodes require two hosts Nearly all cestodes require two hosts Adult is parasitic in the digestive tract of the vertebrate Adult is parasitic in the digestive tract of the vertebrate Over 1000 species of tapeworms known, infecting almost all vertebrates Over 1000 species of tapeworms known, infecting almost all vertebrates Most tapeworms do little harm to host Most tapeworms do little harm to host Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Taenia saginata: Beef Tapeworm Lives as an adult in the digestive canals of humans Lives as an adult in the digestive canals of humans Juvenile form found in intermuscular tissue of cattle Juvenile form found in intermuscular tissue of cattle Mature adults can reach over 10 meters in length with over 2000 proglottids (segments conaining reproductive organs) Mature adults can reach over 10 meters in length with over 2000 proglottids (segments conaining reproductive organs) Scolex has four suckers but no hooks Scolex has four suckers but no hooks Gravid proglottids (with shelled, infective larvae) pass in feces, single Gravid proglottids (with shelled, infective larvae) pass in feces, single Proglottids rupture as they dry Proglottids rupture as they dry Embryos are viable for five months and are picked up by grazing Embryos are viable for five months and are picked up by grazing Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Beef Tapeworm Life Cycle - Continued Cattle swallow shelled larvae that hatch as oncospheres Cattle swallow shelled larvae that hatch as oncospheres Oncospheres use hooks to burrow through the intestinal wall into blood or lymph vessels Oncospheres use hooks to burrow through the intestinal wall into blood or lymph vessels When they reach voluntary muscle, they encyst to become “bladder worms” (cyst that resembles a bladder) When they reach voluntary muscle, they encyst to become “bladder worms” (cyst that resembles a bladder) When the infected meat is eaten, the cyst wall dissolves and the scolex evaginates to attach to intestinal wall When the infected meat is eaten, the cyst wall dissolves and the scolex evaginates to attach to intestinal wall Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display New proglottids develop in 2–3 weeks New proglottids develop in 2–3 weeks Infected individuals expel numerous proglottids daily Infected individuals expel numerous proglottids daily Infection can be avoided by eating only thoroughly cooked beef Infection can be avoided by eating only thoroughly cooked beef Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Life Cycle of Beef Tapeworm: From human feces, to grass, to cattle, to meat, to human.

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Other types of Tapeworm: Taenia solium: Pork Tapeworm Taenia solium: Pork Tapeworm Diphyllobothrium latum: Fish Tapeworm Diphyllobothrium latum: Fish Tapeworm Echinococcus granulosus: Echinococcus granulosus: Unilocular Hydatid Phylum Platyhelminthes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Dog Tapeworm: humans acquire disease by unsanitary habits associated with dogs. When eggs are ingested, larvae encyst in the liver, lungs, or other organs. Cyst enlarges up to the size of a basketball.