Kingdom Animalia Subkingdom Eumetazoa Bilateria Phylum Platyhelminthes

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1 Kingdom Animalia Subkingdom Eumetazoa Bilateria Phylum Platyhelminthes Professor Andrea Garrison Biology 3A Illustrations 2014 Cengage Learning unless otherwise noted

2 Phylum Platyhelminthes Flat worms (platy = flat; helminth = worm) Freshwater, marine, moist soil, parasitic Triploblastic Protostomes Bilateral w/cephalization Body dorsal-ventrally flattened Dugesia sp. Platyhelminthes; photo by Eduard Solà; 2

3 Phylum Platyhelminthes Organ systems Acoelomate Organs embedded in mesoderm Platyhelminthes 3

4 Organ systems Incomplete Y-shaped gut Ladder-like nervous system w/2 anterior ganglia Reproductive system well developed Hermaphroditic Sexual Asexual (fission) Excretory system Flame cells for osmoregulation Platyhelminthes 4

5 Phylum Platyhelminthes No respiratory or circulatory systems Diffusion Body very thin No skeletal system 2-3 muscle layers in body wall Circular, longitudinal, sometimes oblique Pseudobiceros bedfordi. Coral Sea Platyhelminthes; photo by Richard Ling; 5

6 Phylum Platyhelminthes 4 classes Turbellaria free living Trematoda endoparasites Monogenoidea ectoparasites on fish; no further discussion Cestoda endoparasites Platyhelminthes 6

7 Class Turbellaria Free living Most marine Epidermis produces cilia and mucus Locomotion Glide on mucus using muscles and cilia Swim via undulating muscle movements Chemo- and tactile sensors all over body Ocelli Light sensitive Dugesia sp. Platyhelminthes; top photo by Eduard Solà; 7

8 Class Turbellaria Digestive tract Mouth in center of ventral surface Pharynx leads to Y-shaped gut Varying degrees of branching Wrap body around prey Pharynx sucks up bits of food Intestine releases digestive enzyme for extracellular digestion Phagocytes in gastrodermis engulf food Digestion completed inside cells of gastrodermis Platyhelminthes 8

9 Class Turbellaria Reproduction Sexual Copulate w/ another individual Both fertilized by the other Platyhelminthes 9

10 Classes Trematoda & Cestoda Parasitic flatworms Platyhelminthes 10

11 Parasitic Lifestyle Parasitism special physical/nutritional relationship (symbiosis) where one organism benefits and the other is harmed What makes a good parasite? Don t kill host No place else to live May weaken host Adaptations for living on/in host Often have elaborate life cycles Platyhelminthes 11

12 Adaptations for Parasitism Don t kill host directly Hooks/suckers for attachment Extensive reproductive system chances of offspring surviving Endoparasites Glands for penetrating tissues and/or encysting when environment not good Intestinal parasites Tough integument Simple digestive tract Life cycles with many hosts Platyhelminthes 12

13 Parasitic Life Cycle Often multiple hosts Hosts may be from very different phyla Each stage of parasite life cycle often require very specific genus or species of host Definitive host Parasite reaches final stage of development Sexual reproduction occurs here Intermediate host(s) Various stages of the parasite life cycle live in these hosts May be the vector of transmission to final host Platyhelminthes 13

14 Preventing Parasitic Diseases Can treat parasitic diseases like liver flukes, trichinosis Done as the disease arises in the population Prevent parasitic diseases by preventing/avoiding presence of the intermediate hosts Far better for human health Platyhelminthes 14

15 Class Trematoda Flukes Endoparasites; liver, blood, lungs, gut of vertebrates Multihost life cycle Poorly developed sense organs 2 suckers for attachment Oral and ventral Mouth at anterior end Gut with 2 branches Opisthorchis sinensis (=Clonorchis sinensis, Chinese liver fluke) Platyhelminthes 15

16 Class Trematoda Chinese Liver Fluke Common in Asia Definitive hosts humans, cats, dogs, pigs Hermaphroditic Cause: eating raw or undercooked fish, crab Can severely damage liver (cirrhosis) Opisthorchis sinensis (=Clonorchis sinensis, Chinese liver fluke) Platyhelminthes 16

17 Class Trematoda Chinese Liver Fluke Platyhelminthes; 17

18 Class Trematoda Blood Flukes 3 Schistosoma sp. Disease = schistosomiasis Major infectious disease worldwide Cause: working or swimming in infested water Definitive hosts Humans, dogs, cats, rodents, pigs, horse and goats Blood flukes not hermaphroditic Male much larger Female smaller and lives in grove on ventral surface of male Platyhelminthes 18

19 Class Trematoda Schistosomiasis Platyhelminthes: 19

20 Class Trematoda Schistosomiasis Swimmer s itch (cercarial dermatitis or Schistosoma dermatitis) If aquatic larval stage burrows into host of wrong species, it will die Humans may have an allergic reaction to the dead parasite Rash, itching Platyhelminthes 20

21 Class Cestoda Tapeworms Endoparasites; intestines of vertebrates Multihost life cycle No sensory organs Do have sensory receptors in integument Platyhelminthes 21

22 Class Cestoda No gut External body surface covered with microscopic projections Enlarge surface area for absorption Body with proglottids Repeated segments of reproductive structures Hermaphroditic Thousands of fertilized eggs in each Platyhelminthes 22

23 Class Cestoda Scolex at anterior end Hooks and suckers for attachment to intestinal wall Platyhelminthes 23

24 Class Cestoda Life Cycle At least two hosts Definitive host is vertebrate Intermediate host may be invertebrate or vertebrate Infections usually have few symptoms One species can migrate to brain and cause seizures Taenia sp. Eating undercooked beef or pork Crowded, unsanitary conditions Platyhelminthes 24

25 Class Cestoda Taenia sp. Platyhelminthes; 25

26 Class Cestoda Echinococcus Echinococcus granulosis Definitive host dogs eat infected meat raw Intermediate host sheep, goats, swine, cattle, horses, camels Larvae migrate to organs (esp. liver, lungs) Humans in contact with dogs may accidentally ingest eggs Hydatidosis Damage to liver, lungs, heart, bones Platyhelminthes 26

27 Class Cestoda Echinococcus Platyhelminthes 27