Ambulacral grooves are absent in the living forms of the class

Options

A. crinoidea
B. asteroidea
C. ophiuroidea
D. echinodermata

Explanation

To solve the question regarding which class of living forms lacks ambulacral grooves, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Terminology**:
- **Ambulacral grooves**: These are grooves that run along the arms of certain echinoderms, containing tube feet used for locomotion and feeding.
- **Echinodermata**: This is a phylum that includes marine animals like starfish, sea urchins, and sea cucumbers.

2. **Identify the Classes of Echinodermata**:
- The main classes of echinoderms include:
- **Crinoidea**: Sea lilies and feather stars.
- **Asteroidea**: Starfish.
- **Ophiuroidea**: Brittle stars and basket stars.
- **Echinoidea**: Sea urchins and sand dollars.

3. **Analyze Each Class for the Presence of Ambulacral Grooves**:
- **Crinoidea**: Have ambulacral grooves.
- **Asteroidea**: Have ambulacral grooves.
- **Echinoidea**: Have ambulacral grooves.
- **Ophiuroidea**: Do not have ambulacral grooves.

4. **Conclusion**:
- Since ambulacral grooves are absent in the class **Ophiuroidea**, this is the correct answer.

### Final Answer:
The class in which ambulacral grooves are absent in living forms is **Ophiuroidea**.

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