Ambulacral grooves are absent in

Options

A. Asteroidea
B. Crinoidea
C. Ophiuroidea
D. Starfish

Explanation

### Step-by-Step Solution:

1. **Understanding the Term "Ambulacral Grooves":**
- Ambulacral grooves are structures found in echinoderms, specifically in the phylum Echinodermata. These grooves are important for locomotion and are typically located on the oral side of the organism.

2. **Identifying Where Ambulacral Grooves Are Found:**
- Ambulacral grooves are present in various classes of echinoderms, such as Asteroidea (starfish) and Crinoidea. In these organisms, the grooves are lined with tube feet that aid in movement.

3. **Identifying the Exceptions:**
- While most echinoderms have these grooves, there are exceptions. The class Ophiuroidea, which includes brittle stars, is known for lacking ambulacral grooves.

4. **Conclusion:**
- Based on the information, we conclude that ambulacral grooves are absent in Ophiuroidea (brittle stars).

### Final Answer:
Ambulacral grooves are absent in **Ophiuroidea**.

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