Question

The ciliated embryophore of Diphyllobothrium latum is called as

• A. Miracidium
• B. Procercoid
• C. Hexacanth embryo
• D. Coracidium

Hint:

The coracidium stage is unique to pseudophyllidean tapeworms.
It serves the same ecological function as the miracidium of flukes, allowing the parasite to swim and find its first aquatic host.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Diphyllobothrium latum (the broad fish tapeworm) belongs to the order Pseudophyllidea.
Unlike cyclophyllidean tapeworms, pseudophyllideans require an aquatic environment and intermediate hosts for their larval development, which involves a free-swimming ciliated stage.
Detailed Explanation:
Let us review the developmental stages of Diphyllobothrium latum:
- The eggs of D. latum are discharged in feces and must reach fresh water to develop.
- Inside the egg, an oncosphere (hexacanth embryo) develops.
- This oncosphere becomes surrounded by a ciliated outer membrane called the embryophore.
- When the egg hatches, this ciliated, free-swimming larval stage emerges into the water. This stage is called the coracidium.
- The coracidium is ingested by the first intermediate host, a copepod crustacean (such as Cyclops), where it sheds its ciliated coat and develops into a procercoid.
- When the copepod is eaten by a fish (second intermediate host), the procercoid develops into a plerocercoid (sparganum) in the fish muscles.
- Miracidium is the ciliated, free-swimming larval stage of trematodes (flukes), not cestodes.

Step 2: Final Answer:
The ciliated embryophore of Diphyllobothrium latum is called the coracidium.