**Core Concept**
Subterminal spores are a type of spore formation in certain bacteria, where the spores are located at the end of the bacterial cell but not at the very end. This type of spore formation is characteristic of certain species of Clostridium, a genus of Gram-positive, anaerobic bacteria.

**Why the Correct Answer is Right**
Subterminal spores are formed by bacteria that have a complex life cycle, allowing them to survive in harsh environments. These spores are formed by the bacterial cell differentiating into a highly resistant, dormant structure that can withstand extreme temperatures, radiation, and chemicals. The presence of subterminal spores is a key characteristic used to identify certain species of Clostridium.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a correct genus or species of bacteria that form subterminal spores.
* **Option B:** This option is incorrect because it refers to a different type of spore formation, where the spores are located at the very end of the bacterial cell.
* **Option C:** This option is incorrect because it refers to a different genus of bacteria that does not form subterminal spores.

**Clinical Pearl / High-Yield Fact**
Clostridium species that form subterminal spores, such as Clostridium difficile, are known to cause severe gastrointestinal infections in humans. These infections can be life-threatening if left untreated.

**Correct Answer:** B. Bacillus.