Platyhelminthes PDF

‫شعبة المفلطحات‬ Platyhelminthes  Phylum Platyhelminthes Characteristics of the phylum - Acoelomate. with organs - Body wall consists of three layers - Flattened body. bilaterally symmetrical - All hermaphrodites (except Shistosoma) - Free living/ parasitic animals -...

‫شعبة المفلطحات‬ Platyhelminthes  Phylum Platyhelminthes Characteristics of the phylum - Acoelomate. with organs - Body wall consists of three layers - Flattened body. bilaterally symmetrical - All hermaphrodites (except Shistosoma) - Free living/ parasitic animals - No respiratory system; respiration by simple diffusion  Phylum Platyhelminthes Characteristics of the phylum - Excretory system consists of flame cells collect excess water and excretory wastes connected to excretory tubules open to outside. - With cephalized nervous system ; a pair of cerebral ganglion at anterior end and 2 longitudinal nerve fibers connected transversely.  ‫المفلطحات‬Metazoa Subkingdom ‫تصنيف شعبة‬ Phylum Platyhelminthes ‫طائفة التربالريا‬ ‫طائفة الديدان‬ ‫طائفة الديدان‬ class ‫الورقية‬class ‫الشريطية‬class turbellaria trematoda cestoda  Class Turbellaria Includes worms which are free living in salt water or fresh water. It looks like a plant leaf, covered by cilia and have suckers. Planaria: - Lives in fresh water, - hide between water plants and under rocks and prevents the light. - It has a dorsal surface which direct upwards and a ventral surface which direct downwards. Class Turbellaria Gastrovascular cavity Feed on decaying plant or animal matter. Food ingested by a pharynx at middle of body , leads to branched gastrovascular cavity with 3 caeca , secrete digestive enzymes and absorb nutrients. Excretory system A network of excretory tubules ended with flame cells (movement of their cilia similar to candle flame ). Flame cells collect excess water and excretory wastes into the excretory tubules , which open to outside through excretory pores scattered over the body surface Nervous system , Cephalized 2 cerebral ganglia at anterior end , and 2 lateral longitudinal nerves connected transversely by nerves fibres (ladder-like arrangement ) Sense organs: Two cup-shaped eyespots near cerebral ganglia Sexual Reproduction: Hermaphrodites they have both male sex organs (testes ) and female sex organs (ovaries ). When 2 worm mate , they simultaneously fertilize each other fertilized eggs laid in protective capsules that stick to rocks and eggs hatch in 2-3 to weeks Asexual Reproduction (Regeneration) by fission in summer. Posterior part of worm attaches to a surface and the body constricts just behind the pharynx ; anterior part of body moves forward until the worm splits into two ; each half regenerates its missing parts to produce a complete planaria  Class Trematoda (flukes) ( - Body leaf-like , unsegmented - Usually have 2 sucker: oral sucker around the mouth ventral sucker on the ventral surface for attachment - Gastrovascular cavity usually bifurcates into 2 intestinal caeca - - All parasitic - All hermaphroditic except Shistosoma Class Trematoda (flukes) (  Lifecycle of Fasciola gigantica starts when a female lays eggs in the liver of an infected human. Immature eggs are discharged in the biliary ducts and taken out in the feces. If landed in water, the eggs become embryonated and develop larvae called miracidia (which is conical in shape covered by cilia, has short gut and 2 eye spots and a pair of flame cells). Miracidium invades an aquatic snail (Lymnaea) and develops into cercaria, a larva that is capable of swimming with its large tail.. https://www.youtube.com/watch?v=KaZwZ3LKC-A Live Cycle: The metacercaria excises in the first part of the small intestine, duodenum. It then penetrates the intestinal wall and gets into the peritoneal cavity. It finds the liver and starts eating liver cells. This happens only a few days after the initial contact with the parasite. Usually the larva spends a few weeks just browsing and eating the liver. Then it relocates to the bile duct where it begins its final stage and becomes an adult. It takes about three months for the metacercaria to develop into an adult. Typically, the life cycle includes 7 stages