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PHYLUM PLATYHELMINTHES

PHYLUM PLATYHELMINTHES. FLAT BODIED WORMS Class Turbellaria (planarians) mostly predatory free living Class Trematoda (internal flukes) only parasitic complex life-cycles Class Cestoda (tapeworms) only parasitic. EXAMPLES. PLANARIA – FREE LIVING – AQUATIC AND TERRESTRIAL

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PHYLUM PLATYHELMINTHES

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  1. PHYLUM PLATYHELMINTHES FLAT BODIED WORMS Class Turbellaria (planarians) mostly predatory free living Class Trematoda (internal flukes) only parasitic complex life-cycles Class Cestoda (tapeworms) only parasitic

  2. EXAMPLES • PLANARIA – FREE LIVING – AQUATIC AND TERRESTRIAL • Herbivore, carnivore, scavenger • TAPEWORMS – INTESTINAL PARASITE W/ MORE THAN 1 HOST TAENIA • FLUKES – INTERNAL PARASITE W/MORE THAN ONE HOST • BLOOD FLUKE SCHISTOSOMA • LIVER FLUKE FASCIOLA

  3. TRAITS • ORGAN LEVEL OF ORGANIZATION • BILATERAL SYMMETRY • SAC TYPE BODY – 1 OPENING/ no anus • GASTROVASCULAR CAVITY IS BRANCHED • TRIPLOBLASTIC – 3 GERM/tissue LAYERS • CEPHALIZATION – has a head • BRAIN WITH 2 NERVE CORDS & TRANSVERSE NERVES • SENSE ORGANS – light and chemicals • Occeli/eyespots and auricles/ears

  4. TRAITS • ACOELOMATE – no coelom/body cavity • DIFFUSION METHODS FOR: • GAS EXCHANGE - O2 and CO2 • WASTE REMOVAL – by FLAME CELLS • CIRCULATION of nutrients and waste • REMEMBER: DIFFUSION IS A SLOW PROCESS; HI TO LO

  5. Epidermis/ ECTODERM gut cavity Lining of gut =ENDODERM no body cavity; region between gut and body wall packed with organs within MESODERM tissue Acoelomate organism (flatworm) Body Plan

  6. TRAITS • MUSCLES FOR LOCOMOTION • REPRODUCTION • ASEXUAL – REGENERATE • SEXUAL – HERMAPHRODITES BUT CROSS FERTILIZE

  7. EVOLUTIONARY MILESTONE • ORGAN LEVEL OF ORGANIZATION • reproductive, excretory, muscular • BILATERAL SYMMETRY • CEPHALIZATION • Anterior and posterior • Dorsal and ventral

  8. Platyhelminthes Taxonomy Classes of Phylum Platyhelminthes

  9. --Widely distributed in N. America • -- about 200 species • --Occur in both lakes and streams • -- Stream-dwelling species more differentiated than lake species • --Species diversity increases in temperate areas 20 to 60 species per lake Planaria Class Turbellaria

  10. Class Turbellaria • Free-living flatworms; mostly marine • microscopic to two feet • Locomotion in Turbellaria • move by means of cilia and mucous • 2 layers of muscle; longitudinal and circular • Stimulated by nervous system • contractions for turning, twisting and folding of the body

  11. Nutrition in Turbellaria • carnivores and predators of other animals or dead remains. • muscular pharynx is inserted into prey • Secretes digestive enzymes • Fragments are pumped into mouth on ventral surface • Further digestion in gastrovascular cavity • branching increases the surface area for digestion and absorption • No anus, only mouth; • Undigested food excreted from mouth and pharynx as in cnidaria • GVC aids both digestion and circulation – distributes nutrients and oxygen to tissues

  12. Brain/ganglia nerve cords Sensory/nervous • Exhibits cephalization • Group of nerve tissue (GANGLIA) at anterior • Ganglia attached to 2 nerve chords • well developed sensory eyespots for light • auricles for chemical and mechanical (touch) receptors

  13. Reproduction in Turbellaria • Asexual--- • By fission or dividing • Regeneration of missing parts • Sexual- • hermaphrodites w/ cross-fertilization • Internal fertilization • Zygote released to water testis penis genital pore ovary oviduct

  14. EXCRETION IN TURBELLARIA Excretory pore Flame cells Excretory tubules Excretory System pharynx (protruded) protonephridia flame cell nucleus cilia • Cilia of flame cells remove excess water and nitrogen wastes of body • Waste moves to tubules • Exits out pores in head • Needs excretory system as tissues become thicker and more cells present fluid filters through membrane folds opening of tubule at body surface flame cell

  15. Class Trematoda – the Flukes COMMON EXAMPLE OF COMPLEX LIFE CYCLE

  16. Class Trematoda • live as parasites • protected from digestion by protein coat • 2 suckers: • 1. Oral sucker attaches to organs of the host • 2. Ventral sucker or acetabulumattaches to host tissues

  17. Types of Hosts • Complex life cycles • Alternate between sexual and asexual stages • Most require at least 2 different kinds of hosts to complete their life cycle • 1.Definitive host (primary host) • where parasite matures and reproduces (sexually) • host in which eggs are released • 2. Intermediate host • Hosts in which larval stages develop and undergo asexual reproduction • Results in an increase in the number of the individuals

  18. Schistosoma • a common blood fluke of SE Asia • causes shistosomiasis • Definitive host = humans • Intermediate host = snails • In humans - eggs penetrate and damage intestinal and bladder tissue • constant inflammation and eventual deterioration of liver, spleen and other organs Fluke Life Cycle

  19. General Life Cycle - Chinese liver fluke, Clonorchis sinensis • Adults live in the bile ducts of humans, dogs, and cats • There are 2 intermediate hosts: a snail and a fish • Eggs are passed out of the definitive host and hatch as ciliated larvae called miracidia • The miracidia penetrates a snail molluscan host and becomes a sporocyst • They undergo asexual reproduction producing larvae called rediae • Rediae often asexually produce more rediae, but will eventually give rise to larvae called cercariae • They leave the molluscan host and penetrate fish • They encyst in the fish tissues as the metacercaria • Consumption of infected fish results in the metacercaria excysting in the gut and migrating to the bile duct

  20. Class Cestoda • Protective protein coat • anterior region is called a scolex; • oftenarmed with suckers and hooks • Extending from neck of scolex is a series of proglottids; • contain sex organs and eggs; • no digestive system • Mature eggs released through an opening in the proglottid • leave the host when the proglottids break off

  21. b A definitive host eats infected, undercooked beef a Larvae become encysted in intermediate host tissues c Scolex of larva attaches to intestine’s wall d Many proglottids form by budding f Cattle may ingest embryonated eggs or ripe proglottids to become intermediate hosts e Ripe proglottids containing fertilized eggs leave host in feces Class Cestoda Tapeworm Lifecycle

  22. Beef Tapeworm, Taeniarhynchus saginatus • Definitive host = humans; • intermediate host = cattle • Eggs are shed with human feces; • infected persons defecate in a pasture or untreated sewage • eggs are ingested by cattle • Eggs hatch • larvae bore into intestinal wall • get into the circulatory system • transported to muscle • If uncooked beef is consumed the larvae is freed • scolex develops, forming the adult • Symptoms include loss of weight, chronic indigestion, diarrhea

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