Which of the following is not a characteristic of the phylum Annelida ?

Options

A. Hydrostatic skeleton
B. Segmentation
C. Pseudocoelom
D. Closed circulatory system

Explanation

To determine which of the following is not a characteristic of the phylum Annelida, we will analyze each option provided:

1. **Hydrostatic Skeleton**:
- Annelids possess a hydrostatic skeleton, which is formed by the fluid-filled coelom. This allows them to move by coordinating muscle contractions against the fluid pressure. Therefore, hydrostatic skeleton is a characteristic of Annelida.

2. **Segmentation**:
- One of the defining features of Annelids is segmentation. Their bodies are divided into a series of segments, which allows for more complex movement and the specialization of body regions. Thus, segmentation is also a characteristic of Annelida.

3. **Pseudocoelom**:
- Annelids have a true coelom, which is a body cavity completely lined by mesoderm. A pseudocoelom is a body cavity that is not completely lined by mesoderm. Since Annelids do not possess a pseudocoelom but rather a true coelom, this option is not a characteristic of the phylum Annelida.

4. **Closed Circulatory System**:
- Annelids have a closed circulatory system where blood is contained within vessels. This is another characteristic of Annelida.

Based on the analysis, the option that is not a characteristic of the phylum Annelida is **Pseudocoelom**.

### Final Answer:
**Pseudocoelom** is not a characteristic of the phylum Annelida.

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