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Class Trematoda Notes
- 2. Flukes, like tapeworms, are parasites of vertebrate animals. The anterior end of this one is at the top of the photograph. The black “squiggly” lines are excretory ducts that collect wastes from cells and excrete them. The dark bow-shaped lines that extend from anterior to posterior, are longitudinal nerves. Flukes are round to football- shaped, but the head is always a bit pointed.
- 3. 1 2 3 1 Ganglion – it is the flatworm’s primitive brain and is formed by the fusion of the two longitudinal nerves. 2 Longitudinal nerves extend the length of the flatworm’s body on both sides. 3 Transverse nerves branch towards the ectoderm from the transverse nerve.
- 4. Fluke life cycles are complex and usually involve two hosts, one is for the adult fluke (in this diagram a cow or sheep) and is called the definitive or primary host. The intermediate host is infested by the fluke’s larvae (a snail in the case of the sheep liver fluke). Liver flukes live and reproduce in the bile duct (duct from gall bladder to liver). Notice that there are two larval stages (the miracidium and the cercariae). This fluke evolved with sheep and snails. All flukes have similarly complex life cycles that include two larval forms and multiple hosts.
- 5. The Chinese liver fluke is a human parasite. Its intermediate hosts include snails and fish. Humans become infected by eating raw or poorly cooked fish. In some fishing villages in southeast Asia, medical tests have proven that 100% of the human residents are infested because the people’s diet includes raw fish. In such villages, human feces are often dumped into the same waters that fishes are taken from as a food source.
- 6. The End