Question

Which larval form of {Fasciola hepatica has a motile tail?}

• A. Miracidium
• B. Redia
• C. Sporocyst
• D. Cercaria

Hint:

Remember the motile stages in the fluke life cycle:

\textbf{Miracidium}: Motile by \textbf{cilia}.
\textbf{Cercaria}: Motile by a \textbf{tail}. \end{itemize} The stages inside the snail (Sporocyst, Redia) are non-motile sacs for asexual reproduction.

Answer 1

The Correct Option is D

Step 1: Concept Overview:
*Fasciola hepatica*, the liver fluke, has a complex life cycle with several larval stages and a snail intermediate host. The question requires identification of the larval stage characterized by a motile tail used for locomotion.

Step 2: Larval Stage Details:
The life cycle stages are:
1. Miracidium: The first larval stage, hatching from the egg in freshwater. It's a free-swimming larva, motile via cilia covering its body, not a tail. It seeks a snail host to penetrate.
2. Sporocyst: Inside the snail, the miracidium transforms into a non-motile sporocyst. It reproduces asexually, forming more sporocysts or rediae.
3. Redia: Developing within the sporocyst, the redia has a mouth and pharynx, more developed than the sporocyst, but remains non-motile within the snail. It reproduces asexually, producing more rediae or cercariae.
4. Cercaria: This larval stage exits the snail into the water. It has a distinct body and a long, powerful tail used for swimming to find aquatic vegetation for encystment.
5. Metacercaria: The cercaria loses its tail and encysts on vegetation, becoming the metacercaria, the infective stage for the final host (e.g., sheep, cattle, humans).

Step 3: Conclusion:
The Cercaria is the only larval stage with a distinct, motile tail for swimming. Therefore, option (D) is correct.