Which of the following statements is incorrett about sea walnuts?

Options

A. They are diploblastic animals
B. They exhibit tissue-level of organisation
C. They undergo indirect development
D. Fertilisation is internal

Explanation

To determine which statement about sea walnuts is incorrect, we can analyze each statement based on the characteristics of these organisms.

### Step-by-Step Solution:

1. **Identify the Organism**: Sea walnuts belong to the phylum Ctenophora. It is important to note that they are often confused with other marine organisms, so confirming their classification is essential.

2. **Check Diploblastic Nature**: Sea walnuts are indeed diploblastic, meaning they have two germ layers: ectoderm and endoderm. This statement is correct.

3. **Tissue Level of Organization**: Sea walnuts exhibit a tissue level of organization. This means they have specialized cells that form tissues. This statement is also correct.

4. **Development Type**: Sea walnuts undergo indirect development, which involves a larval stage before reaching maturity. This statement is correct.

5. **Fertilization Method**: The fertilization in sea walnuts is external, meaning that the sperm and eggs are released into the water where fertilization occurs. If any option states that fertilization is internal, that would be incorrect.

6. **Conclusion**: After analyzing all the statements, the one that claims fertilization is internal is incorrect. Therefore, this is the answer to the question.

### Final Answer:
The incorrect statement about sea walnuts is that fertilization is internal.

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