The water-snail is important in the life cycle of the liver fluke. Liver flukes are parasitic flatworms that cause a disease called fascioliasis in the liver of various mammals, including humans, cattle, and sheep.
Here is a simple explanation of how the water-snail fits into the liver fluke's life cycle:
1. Egg Stage: The adult liver fluke lives in the host's liver and produces eggs, which are excreted in the host's feces.
2. Miracidium Stage: These eggs hatch in a water environment into larval forms called miracidia.
3. Snail Host: The miracidia must find and penetrate a specific species of freshwater snail. The water-snail serves as the intermediate host where the liver fluke undergoes a significant part of its development.
4. Sporocyst, Rediae, and Cercariae Stages: Inside the snail, the liver fluke develops through several stages: sporocysts, rediae, and cercariae.
5. Free-swimming Cercariae: The cercariae leave the snail and enter the water, seeking to attach to aquatic plants or other surfaces.
6. Metacercariae on Plants: The cercariae encyst to form metacercariae on these plants, waiting to be ingested by the next mammalian host.
Thus, the water-snail plays a crucial role as an intermediate host, enabling the fluke to transform into forms that are ready to infect mammals. Without the snail, the liver fluke's life cycle cannot continue.