Biology 11

Ms. Jamieson

ParasiticWorms

Characteristics of Platyhelminthes

  • bilaterally symmetrical withcephalization
  • dorsoventrally flattened
  • highly branched gastrovascular cavity with only one opening, which serves the function of both the mouth and anus
  • 3 cell layers:
  • Ectoderm: Outside
  • Endoderm: Inside
  • Mesoderm: Middle layer of tissue between the ectoderm and the endoderm
  • Acoelomate with no body cavity

3 Classes of Platyhelminthes

  • Turbellaria - Free-living Flatworms (carnivores and scavengers)
  • Trematoda - Flukes (parasites)
  • Cestoda - Tapeworms (parasites)

Adaptations of Parasitic Flatworms

Trematoda - Flukes

  • The fluke has an anterior end with an oral suckeraround its mouth and a pharynx
  • Fluke also have abody covering called a tegument, which is made of modified ectoderm that protects it from their host’s immune system and digestive juices
  • The tegument also functions in gas exchange and absorbing nutrients
  • Other than these adaptations flukes show many of the same characteristics as the free-living Flatworms
  • Most parasitic flukes have very complicated life cycles

Cestoda - Tapeworms

  • The tapeworm has an anterior end called a scolex with complicated hooks for attaching to the intestines of its host.
  • The tapeworm does not have a mouth or digestive system. Instead they bath in the pre-digested fluids of their host and absorb nutrients directly into their body cells by diffusion
  • Like flukes, tapeworms have a modified ectoderm called a tegumentwhich function in protection, gas exchange and nutrient absorption
  • Tapeworms are hermaphroditic
  • the body is segmented into proglottids, each containing male and femalesexual organs.
  • As the eggs in the proglottidsmature, the proglottidsare released into the human host’s intestines and eventually end up in the host’s fecal matter.

Characteristics of Nematoda

  • bilateral symmetry
  • a complete digestive systemwith a mouth and an anus connected by intestines
  • three germ layers:
  • Ectoderm
  • Endoderm
  • Mesoderm
  • A cuticle made of collagen is secreted by the epidermis and surrounds the body. It functions in protection and as an exosketon that gives the worm its shape
  • pseudocoelomates - have an internal body cavity that is not lined with mesoderm
  • The body is round and unsegmented

Free-Living and Parasitic Nematodes

  • Nematodes are found in every habitat on the planet from marine to fresh water, the polar regions to the tropics and from the highest elevations to the lowest.
  • May be free-living or parasitic
  • Free-living Nematodes eat bacteria, fungi, protozoans and decomposing material
  • Parasitic Nematodes live off their host organism

Adaptations of Parasitic Nematodes

  • Mostly parasitic on vertebrates and can cause serious illness.
  • Have very complicated lifecycles.

Life cycle of Trichinellaspiralis

Primary Host = ______and Secondary Host = ______

Method of Infection = ______