Which of the following groups of organisms is a radially symmetric deuterostome ?

Options

A. Echinoderms
B. Chordates
C. Arthropods
D. Molluscs

Explanation

To solve the question "Which of the following groups of organisms is a radially symmetric deuterostome?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Terms**:
- **Deuterostome**: This is a group of animals characterized by their embryonic development. In deuterostomes, the first opening (blastopore) becomes the anus, while the mouth forms later.
- **Radial Symmetry**: This means the organism can be divided into similar halves by multiple planes passing through the central axis.

2. **Identify the Groups**:
- The options provided are:
A. Echinoderms
B. Chordates
C. Arthropods
D. Sage mollusks

3. **Classify the Groups**:
- **Echinoderms**: These include organisms like starfish and sea urchins. They are deuterostomes and exhibit radial symmetry in their adult forms.
- **Chordates**: This group includes vertebrates like mammals, birds, and fish. They are deuterostomes but have bilateral symmetry, not radial.
- **Arthropods**: This group includes insects, arachnids, and crustaceans. They are protostomes, not deuterostomes.
- **Sage Mollusks**: This group includes snails, clams, and octopuses. They are also protostomes.

4. **Determine the Correct Answer**:
- Since echinoderms are the only group listed that is both a deuterostome and exhibits radial symmetry, the correct answer is **A. Echinoderms**.

### Final Answer:
The group of organisms that is a radially symmetric deuterostome is **A. Echinoderms**.

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