**Core Concept**
Ergot alkaloids are a group of compounds derived from the ergot fungus (Claviceps purpurea) that have various pharmacological effects, including vasoconstriction, uterine stimulation, and sympathomimetic activity. These compounds interact with serotonin receptors and other molecular targets to produce their clinical effects.

**Why the Correct Answer is Right**
To identify the correct answer, we need to review the common ergot alkaloids. Ergotamine, ergonovine, and methylergonovine are classic examples of ergot alkaloids used in clinical practice for their vasoconstrictive and uterine-stimulating properties. Ergotamine is used for migraine prophylaxis and treatment, while ergonovine and methylergonovine are used to prevent and treat postpartum hemorrhage. **Option A**, Ergotamine, is indeed an ergot alkaloid.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incomplete. If complete, it would likely be a different compound.

**Clinical Pearl / High-Yield Fact**
Ergot alkaloids can cause severe vasoconstriction, which can lead to ischemia and gangrene, especially in the digits. This is a critical side effect to remember when prescribing these medications.

**Correct Answer:** B.