Consider the following characteristic features. (a) Closed vascular system (b) External fertilization (c) Dioecious (d) Double ventral nerve cord The above features characterise

Options

A. Leech
B. Earthworm
C. Sandworm
D. Bloodworm

Answer

To solve the question regarding the characteristic features of a specific group of organisms, we will analyze each feature step by step.

### Step-by-Step Solution:

1. **Identify the Features**:
The features given are:
- (a) Closed vascular system
- (b) External fertilization
- (c) Dioecious
- (d) Double ventral nerve cord

2. **Analyze Each Feature**:
- **Closed Vascular System**: This feature is characteristic of organisms in the phylum Annelida, which includes segmented worms.
- **External Fertilization**: Many aquatic organisms, including some annelids, exhibit external fertilization.
- **Dioecious**: This means that the organisms have distinct male and female individuals. While many annelids are monoecious (having both male and female reproductive organs), some, like certain polychaetes, are dioecious.
- **Double Ventral Nerve Cord**: This is a typical feature of annelids, where they have a ventral nerve cord that is double.

3. **Determine the Group**:
Based on the features analyzed:
- The presence of a closed vascular system, external fertilization, and a double ventral nerve cord points towards annelids.
- The dioecious nature suggests we are looking for a specific type of annelid.

4. **Identify Specific Examples**:
- While earthworms and leeches are common examples of annelids, they are generally monoecious.
- However, polychaetes, such as Nereis (often referred to as sandworms), are dioecious and exhibit the other features listed.

5. **Conclusion**:
Therefore, the organism characterized by the features (a) closed vascular system, (b) external fertilization, (c) dioecious, and (d) double ventral nerve cord is the **sandworm (Nereis)**.

### Final Answer:
The above features characterize **Nereis (sandworm)**.

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