2Today’s ObjectiveTSW take notes on the phylum Platyhelminthes including economic importance, an overview of class characteristics, and ecological niches.
3General Flatworm Characteristics Acoelomate – no body cavity coelom- solid mesenchyme (mesoderm)First phylum to show a definite cellular mesodermBilaterally symmetricalTriploblastic; 3 distinct tissue or germ layersDorsoventrally flattened
4General Characteristics (cont.) Respiration by diffusionDigestive system extensively branchedOne opening for feeding and waste removalLack an anusPrimitive kidneys – protonephridia with “FLAME CELLS”
5General Charcterisitcs (cont.) First evidence of cephalization primitive brainSome have eyespotsDirectional movementNo true respiratory system or circulatory systemUsually hermaphroditic
6Class Turbellaria Free-living flatworms Some freshwater (Planaria), marine, or terrestrialMost move by circular and longitudinal musclesSome move by using cilia (or cilia + mucus)
7Turbellarian Feeding - Carnivorous Wrap body around preyEntangling with mucousIngest the whole prey or suck its juices through a hardened stylet (modified pharynx)in many species the pharynx is completely eversible and can envelope the entire preythere is no anus so ingestion and egestion are through the mouth
8Turbellarian Reproduction Sexual ReproductionMost hermaphroditicBoth sex organs discharge gametes into a common chamber even though this is true- cross fertilization is the most common mode of reproductionSome self fertilization can and does occurAsexual ReproductionFragmentation and Regeneration
10Class Monogenea Parasitic Flukes Only one host Most external parasites GyrodactylusPolystomaCan cause major economic losses to fisheries
11Class Trematoda Digenetic Flukes Complex life history, involves 2 or more hostsLive in every type of environment5,000+ known speciesLive mostly in digestive system or associated organs (all parasitic)
12Some Trematodes of Importance Clonorchis – Chinese human liver flukeFasciola hepatica – Liver flukeSchistosoma – Blood flukeKnow this life cycle!Where they are present it is hazardous to bathe, drink, wade in or dip your arms in infested waters!
13Class Cestoda - Tapeworms Long, FlattenedWhite or Yellow in colorAll parasitic!Adults almost always live in the intestines of their hostsBody has protective cuticleHead (scolex) has multiple disks of hooks for attachment
14Cestodes (cont.) Can reach up to 50 ft. in length! No specialized sense organsReproduce using proglottids (segments)Contain flame cells, nerves, muscles, male and female reproductive organsShed in feces of hostTaenia saginata – beef tapewormTaenia solium – pork tapeworm