**Core Concept**
Schistosomiasis, also known as snail fever, is a parasitic disease caused by infection with Schistosoma species. The transmission of schistosomiasis involves a complex life cycle that involves both aquatic and terrestrial hosts. The primary mode of transmission is through contact with contaminated water.

**Why the Correct Answer is Right**
The correct answer is a freshwater snail, specifically species belonging to the genus Bulinus and Planorbis. These snails serve as intermediate hosts for the Schistosoma parasite. The parasite undergoes asexual reproduction within the snail, producing cercariae that are released into the water. Human infection occurs when cercariae penetrate the skin of individuals who come into contact with contaminated water, initiating the infection process.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the primary mode of transmission for schistosomiasis.
**Option B:** This option is incorrect because it does not accurately describe the intermediate host involved in the transmission of schistosomiasis.
**Option C:** This option is incorrect because it does not accurately describe the life cycle of the Schistosoma parasite.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that schistosomiasis transmission is highly dependent on the presence of suitable intermediate hosts, such as freshwater snails, and contaminated water. Understanding the life cycle of the parasite is crucial for developing effective prevention and control measures.

**Correct Answer:** A. Freshwater snail.