Which of the following statement is incorrect about the phylum hemichordata?

Options

A. They are bilaterally symmetrical, triploblastic and coelomate animals
B. Circulatory system is closed
C. Excretory organ is proboscis gland
D. Fertilisation is external and development is indirect

Explanation

To determine which statement is incorrect about the phylum Hemichordata, we can analyze each statement provided.

### Step-by-Step Solution:

1. **Understanding Hemichordata**:
- Hemichordata is a phylum of marine animals that are considered to be more advanced than many other invertebrates. They possess a cylindrical body and exhibit bilateral symmetry.

2. **Germ Layers**:
- Hemichordates have three germ layers: ectoderm, mesoderm, and endoderm. This is a characteristic of more complex organisms, so this statement is correct.

3. **Body Cavity**:
- Hemichordates are coelomate animals, meaning they have a true coelom. This is also a correct statement.

4. **Circulatory System**:
- The circulatory system of Hemichordata is open, not closed. This statement is incorrect and is the answer we are looking for.

5. **Excretory Organs**:
- The excretory organ in Hemichordates is the proboscis gland, which is a correct statement.

6. **Fertilization**:
- Fertilization in Hemichordates is external, meaning that the male and female gametes fuse outside the body. This statement is also correct.

7. **Development**:
- Hemichordates exhibit indirect development, which means they go through a larval stage before reaching adulthood. This statement is correct as well.

### Conclusion:
The incorrect statement about the phylum Hemichordata is that they have a closed circulatory system. The correct answer is that they possess an open circulatory system.

### Final Answer:
The incorrect statement about Hemichordata is that their circulatory system is closed.

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