" The Big Picture!" by Mr C

Biology 11

Name: ______________________ Date: __________ Block: _____

Parasitic Platyhelminthes

(Classes Trematoda, Cestoda and Monogenea)

Parasitic Platyhelminthes are quite a bit different than their free-living relatives. Many of these adaptations are related to the fact that they live within host organisms. Most of the final host organisms that parasitic Platyhelminthes use are vertebrates, including HUMANS!!! However, they have intricate lifecycles with intermediate host organisms.

Here is a list of adaptations that make the fluke and the tape worms different than the free-living flatworms.

Class Cestoda (Tapeworms):

1. The Beef Tapeworm

• The tapeworm has a _______________ at its anterior end, with complicated hooks for attaching to the intestines of its host.
• The tapeworm does not have a _______________ or _______________. They are bathed in the pre-digested fluids of their host, and absorb nutrients directly into their cells
• Since they live in such a harsh environment as the intestines they have a modified ectoderm called a _______________ which protects them from the host’s _______________ and _______________
• The tapeworm is _______________ and has a body adapted for reproducing.
• The body of the tapeworm is segmented into _______________, each containing both male and female _______________.
• As the eggs in the proglottids are fertilized they are released into the human host’s intestines and eventually end up in the host’s _______________.

• Lifecycle:
  • After the fertilized eggs have been released in the fecal matter of the human host the feces can be used as fertilizer etc.
  • The eggs are ingested by the intermediate host, a cow
  • The eggs mature into larva which burrow into the muscles of the cow
  • The beef is eaten by more humans and the larva mature into tapeworms in the intestine of the human host to start the lifecycle again.

Class Trematoda (Flukes):

1. Schistosoma

• The fluke worm has an an _______________ on its anterior end for attaching to the host
• Fluke worms also have a _______________ to protect them from their host’s _______________ and _______________
• Flukes are most often _______________ but in the case of Schistosoma there is a male and a female form
• Other than these adaptations flukes show many of the same characteristics as the free-living turbellarians

• Lifecycle:
  • The adult fluke worm lives in the blood vessels near the intestine of a human host.
  • When it is ready to lay its eggs it pushes its way into one of the tiny blood vessels of the intestine and lays thousands of eggs
  • The sheer number of eggs causes the blood vessels to burst releasing the eggs into the intestine
  • The eggs are carried out of the human host in their fecal matter
  • In many underdeveloped countries there are no proper sewage system and the fecal matter is used as fertilizer
  • The eggs get into the water systems and mature into ciliated larva
  • The larva swim until they find a snail intermediate host. If they do not find this snail they will die
  • The larva burrow into the tissue of the snail, feed on its tissues and asexually reproduce
  • The new larvae exit the snail and become free-swimming
  • The new free-swimming larvae burrow into the skin of humans who are swimming near them
  • A male larva and female larva will find eachother and move through the human circulatory system until they reach the human liver where they mature and feed on red blood cells
  • The pair of mature trematodes migrate to the intestines where they undergo sexual reproduction
  • The female releases the eggs into the small blood vessels of the intestines to start the cycle again.