Environment determines the sex of the animal in
(A) Bonellia
(B) Hirudinaria
(C) Nereis
(D) Both A and B

Options

A. Bonellia
B. Hirudinaria
C. Nereis
D. Both A and B

Answer

To solve the question regarding which animal's sex is determined by the environment, we can follow these steps:

### Step 1: Understand the Question
The question asks which organism's sex is determined by environmental factors. The options provided are:
- (A) Bonellia
- (B) Hirudinaria
- (C) Nereis
- (D) Both A and B

### Step 2: Analyze Each Option
- **Bonellia**: This organism exhibits environmental sex determination. The adult female produces a pigment called bonellin, which influences the sex of the larvae that come into contact with it. If the larvae encounter bonellin, they develop into males.

- **Hirudinaria**: This organism does not have its sex determined by environmental factors. The sex is genetically determined rather than influenced by external conditions.

- **Nereis**: Similar to Hirudinaria, Nereis does not have its sex determined by environmental factors. It also has a genetic basis for sex determination.

### Step 3: Identify the Correct Answer
Since only Bonellia exhibits environmental sex determination, the correct answer is (A) Bonellia.

### Step 4: Consider Other Options
Option (D) states "Both A and B," but since Hirudinaria does not exhibit environmental sex determination, this option is incorrect.

### Final Answer
The correct answer is **(A) Bonellia**.

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