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Worms: Trematoda.
Introduction to Flukes.
Flukes Gallery.

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Worms: Introduction Annelids Nematodes Flatworms Parasitic

  Platyhelminthes. (concluded).

1. Turbellarians. 2. Cestodes. 3. Trematodes.

  The Flukes. (Trematoda).

All flukes are either internal or external parasites of vertebrates. They are of extreme economic importance, especially in tropical developing countries. Bilharzia, or Schistosomiasis, is a disease caused by species of the blood-fluke Schistosoma, and is at present the world's second most prevalent infectious disease -- second only to malaria.
Areas such as Africa (especially Egypt), South America and China are worst affected.

Flukes have flattened, leaf-like bodies, with one or two suckers, through which most species are able to feed. Tapeworms also have suckers, but when present, they serve only for attatchment. The life cycle of flukes differs from one species to another, but always involves a number of larval stages, one of which is invariably spent in a freshwater mollusc -- usually a snail.


The classic fluke of the textbooks is the liver fluke, Fasciola hepatica, which infects a wide range of domestic and wild animals, including sheep and humans.

Click for diagrams of Fasciola showing (a) reproductive system, and (b) nervous and reproductive systems.
The miracidium larva (the first larval stage) of Fasciola is seen in the process of hatching in the movie sequence below. The original footage was shot on 16mm Kodachrome with synchronized electronic flash.

Liver Fluke Larva Hatching.

Click image for larger
(346KB) animation.
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The eggs of the liver fluke are voided along with the faeces of the infected animal, and if they have fallen into water or wet grass, their hatching is stimulated by exposure to light. The sole task of the newly hatched miracidium larva is to find and infect a water snail of the common genus Limnea, within which the second larval stage will develop.

The sequence does not show the egg actually opening, as the exact moment is difficult to anticipate, and colour film is expensive. In the minutes preceding the beginning of the shot, fluid buildup within the egg causes a small circular lid (operculum) to pop open, and the pressure release assists the larva in the initial stage of its escape.
The larva is completely covered with cilia and is capable of sustained energetic swimming, but will soon die if a host snail is not found.
A single prominent eyespot can be seen.

The specimens were provided by the Department of Animal Biology at Imperial College, London, and arrived at Micrographia in a small glass phial completely wrapped in aluminium foil. Hatching began the moment the foil was removed and the phial exposed to light.
Darkfield, x200.

to Tapeworms (Cestoda).
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