Which one is an ophiuroid ?

Options

A. Brittle star
B. Sea Star
C. Sand Dollar
D. Sea Urchin.

Answer

To determine which organism is an ophiuroid from the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the term "Ophiuroid":**
- Ophiuroids are a class of echinoderms known for their distinct body structure and movement. They are commonly referred to as brittle stars or serpent stars.

2. **Analyze the options provided:**
- The options given are:
- A) Brittle star
- B) Sea star
- C) Sand dollar
- D) Sea urchin

3. **Identify the classification of each option:**
- **Brittle star:** Belongs to the class Ophiuroid.
- **Sea star:** Belongs to the class Asteroidea.
- **Sand dollar:** Belongs to the class Echinoidea.
- **Sea urchin:** Also belongs to the class Echinoidea.

4. **Determine which option corresponds to the class Ophiuroid:**
- From the classifications, the brittle star is the only organism that belongs to the class Ophiuroid.

5. **Conclude the answer:**
- Therefore, the correct answer to the question "Which one is an ophiuroid?" is **A) Brittle star**.