Class Trematoda

(flukes)

1. Almost exclusively endoparasitic.
2. Bilaterally symmetrical.
3. Specialized suckers for attachment to host.
4. Flame cells for excretion.

While a few trematodes are exoparasitic, most are endoparasitic. They are simple organisms with a gastrovascular cavity, flame cells for excretion and a nervous system with no special sense organs. One or more well-developed suckers are used to cling to the host organism. A cuticle-like tegument protects trematodes from digestive enzymes and antibodies that are present in the host. The life cycle of these parasites is extremely complicated, generally involving egg and several larval stages and utilizing an array of hosts. Reproduction is sexual.

• Adult trematodes can release up to 20,000 eggs per day.
• The Schistomatidae cause the disease schistosomiasis. This disease can effect humans and become very serious.

1. Marshall, A.J. and W.D. Williams. 1972. Textbook of Zoology: Invertebrates. NY: American Elsevier.
2. Smyth, J.D. 1966. The Physiology of Trematodes. San Fransico: W.H. Freeman and Company.

• Using either Clonorchis or Fasciola as an example, draw on a single page as many as the different stages of the life cycle as can fix and be usable. How do these stages differ in size? How do they differ in complexity.
  
• Along the left side of the page make a sketch of a whole trematode. Along the right side make drawings of selected sections associated with the different regions of the wholemount. Try to imagine what the intervening sections might look like that connect up the ones that you have drawn.