In which group of animals, coelom is filled with blood?

Options

A. Arthropoda
B. Annelida
C. Nematoda
D. Echinodermata

Explanation

**Step-by-Step Solution:**

1. **Understanding Coelom**: Coelom refers to the body cavity that is found in many animals. It is a true body cavity that arises from the mesoderm during embryonic development.

2. **Types of Coelom**: There are different types of coeloms based on their formation. The true coelom is formed by splitting of the mesoderm, known as schizo-coelom.

3. **Identifying Groups of Animals**: The question asks which group of animals has a coelom filled with blood. The main groups to consider are Arthropods, Annelids, Molluscs, Echinoderms, and Chordates.

4. **Blood in Coelom**: In Arthropods, the body cavity contains a fluid known as hemolymph, which is colorless and functions similarly to blood. This cavity is referred to as hemocoel.

5. **Comparing Other Groups**:
- In Annelids, the coelom is present but it is filled with coelomic fluid, not blood.
- In Molluscs (non-cephalopods), the coelom is also present but typically does not contain blood.
- Echinoderms and Chordates have a different formation of coelom and do not have blood filling their coelom.
- Nematodes do not have a true coelom; they have a pseudocoelom which is not filled with blood.

6. **Conclusion**: Based on the information, the group of animals where the coelom is filled with blood is Arthropoda.

**Final Answer**: The group of animals in which the coelom is filled with blood is Arthropoda.

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