platyhelminthes ppt

• Phylum Platyhelminthes (Flatworms)
• Platyhelminthes

  • Size range: mm or less – many meters in length
  • Body may be slender, broadly leaflike, or long & ribbon-like
  • Lifestyle: free-living or parasitic
  • No single, unique characteristic for the phylum as a whole (some says this group is polyphyletic!)
  • Recent molecular phylogenies suggest that this is a group; defining feature: syncytial tegument/ neodermis (?)
• Groups of Platyhelminthes

  • Turbellaria
  • Cestoda
  • Monogenea
  • Trematoda
• Platyhelminthes


  • Body is flattened dorsoventrally
  • Body is acoelomate: 1 body cavity ~ gut, lined by parenchyma
  • Mesoderm has more cells & fibers , less ECM
  • Gut incomplete, may be branched, or absent (in Cestoda)
  • Epidermis may be cellular or syncytial
• Planarian structure


  1. Osmoregulatory & Reproductive system

  2. Nervous system & digestive tract

  3. Pharynx extended from mouth
• Turbellaria


  Mostly aquatic; Approx. 4,500 are free-living, ~150 are parasitic
• Turbellaria


  • Nervous system: w/ cerebral ganglion, w/ 1-3 pairs of longitudinal nerve cords; Bear 1 or more pairs of eyes; w/ variety of sensory receptors
  • Body surface is ciliated!
  • Epidermis possesses rhabdites ~ releases mucus for coating; w/ dual-gland adhesive organs
  • Digestive system is fairly simple; some have protrusible pharynx, other have proboscis
  • Most are carnivores; harbor algal symbiont
  • Possesses remarkable regenerative power
• Turbellaria - Order Macrostomida

  • Lives between sand and water sediments
  • numerous rhabdites, no statocysts
• Turbellaria - Order Polycladida


  • Stylochus ellipticus (Oyster leech)
  • Pseudobiceros hancockanus
• Cestoda (Tapeworms)

  • Most members are endoparasites ~ internal parasites
  • Epidermis: non-ciliated tegument (w/ many nuclei ~ syncytial)/ syncytial tegument
  • Outer surface is outfolded into numerous cytoplasmic projections ~ proglottids = increase surface area for absorption
  • Anterior end: scolex = studded w/ hooks & suckers; for attachment
• Segmentation in cestodes is NOT similar to metamerism found in Annelida, Arthropods, & Chordata
• Cestoda

  • Lack digestive system but have well developed muscles
  • Surface is covered with microtriches (s. microthrix) ~ similar to microvilli of vertebrate small intestine
  • Proglottids form a chain of strobila; each proglottids is involved in sexual reproduction; contains both male and female reproductive organs
  • Monoecious; Simultaneous hermaphrodite
• Cestode life cycle

  1. Proglottids in host

  2. Eggs (fertilized)

  3. Intermediate hosts

  4. Definitive host
• Cestoda - Order Pseudophyllidea


  • Diphyllobothrium latum (Fish tapeworm)
• Cestoda - Order Cyclophyllidea


  • Taenia solium (Pork tapeworm)
  • Taenia saginata (Beef tapeworm)
  • Echinococcus granulosus (Unilocular hydratid)
• T. solium


  Pork tapeworm that can reach 7 m in length
• Taenia saginata is the beef tapeworm
• Taenia saginata


  • Infection is through consumption of infected, undercooked beef
  • Adults typically possess about 1,000 proglottids, but they are rarely exceed lengths of 60 cm (although individuals 3m to 5m have been reported)
  • Infection is far less severe than that associated with infection by the pork tapeworm
• Taenia saginata vs T. solium

  • Lack rostellum and hooks (vs T. solium)
• Echinococcus granulosus


  Unilocular hydratid that reach adulthood in dogs and are rarely larger than about 3 mm, possessing no more than 5 proglottids
• Echinococcus granulosus in humans

  • Larval stage multiply asexually to form hydratid cysts that house many thousands scolices
• Dipylidium caninum is the dog tapeworm that parasitize cats and dogs worldwide and infect humans who ingest the intermediate hosts (fleas and lice)
• Tapeworms


  • Common in birds and mammals, with arthropods as intermediate hosts
• Hymenolepis nana


  Dwarf tapeworm that includes hundreds of species parasitizing birds and mammals, including humans
• Hymenolepis nana infection


  • Most often asymptomatic
  • Heavy infections can cause weakness, headaches, anorexia, abdominal pain, and diarrhea
• Monogenea


  Monogenetic flukes, ectoparasites of fishes (in skin & gills)
• Monogenea


  • Haptor/opisthaptor - highly specialized posterior end for attachment
  • Prohaptor - anterior adhesive organ consisting of suckers & adhesive glands
  • Show a very high level of host specificity & occupy highly specific sites w/n a host
  • Life cycle: Sexual maturity in host → egg production → larval stage (oncomiracidum) → attachment to fish
• Monogenea


  • Dactylogyrus sp.
  • Gyrodactylus sp.

  
• Trematoda


  Digenetic flukes, all members are parasitic – in or on vertebrate hosts
• Trematoda


  • The body resemble turbellarians (leaflike) but the body is a non-ciliated syncytial tegument
  • Lacks haptors; but have mouth opening & blind-ended digestive tract
  • The body is never segmented
  • Life cycle requires at least 1 intermediate host before reaching the final host
• Trematoda life cycle


  Fertilized egg → ciliated miracidium → Enters/bores into an intermediate host (always a mollusk) → Sporocysts → Redia → Cercaria (free-living) → Metacercariae (encysted stage)
• Blood flukes


  Adults are all parasitic in the blood vessels of mammals and birds, requires 2 hosts only: the mollusk and the vertebrate
• Schistosoma japonicum


  Blood fluke, the cercariae larvae penetrate the skin of humans causing swimmer's itch
• Echinostoma sp.


  • Commonly parasitize the cloaca and intestines of birds and mammals, respiratory systems of birds, intestines of fishes, and the lungs of turtles
  • Pathogenicity likely varies depending on the infecting species
  • Catarrhal inflammation often occurs
  • In heavy infections, gastrointestinal signs/symptoms may occur
  • Peripheral eosinophilia is usually present
  • A small number of fatal cases have been reported
• Fasciola spp.


  Liver flukes, including the common liver fluke Fasciola hepatica and the related parasite F. gigantica
• Fasciola infection


  • People usually become infected by eating raw watercress or other water plants contaminated with immature parasite larvae
  • The pathology typically is most pronounced in the bile ducts and liver
  • Fasciola infection is both treatable and preventable
• Clonorchis sinensis


  Chinese/Oriental liver flukes that infect the liver, gallbladder, and bile duct in humans
• Clonorchis sinensis infection


  • While most infected persons do not show any symptoms, infections that last a long time can result in severe symptoms and serious illness
  • Untreated, infections may persist for up to 25–30 years, the lifespan of the parasite
• Opisthorchis viverrini


  Southeast Asian liver flukes
• Opisthorchis viverrini infection


  • Most infections are asymptomatic
  • Most pathologic manifestations result from inflammation and intermittent obstruction of the biliary ducts
  • In mild cases, manifestations include dyspepsia, abdominal pain, diarrhea, or constipation
  • With infections of longer duration, the symptoms can be more severe, and hepatomegaly and malnutrition may be present
  • In rare cases, cholangitis, cholecystitis, and chlolangiocarcinoma may develop