The presence of mesoderm :

Options

A. restricts the development of a coelom
B. is associated with the organ level of organization
C. is associated with the development of muscles
D. both (b) and (c)

Answer

To solve the question regarding the presence of mesoderm, we will analyze each option provided and determine which statements are accurate based on our understanding of mesoderm in the context of animal development.

### Step-by-Step Solution:

1. **Understanding Mesoderm**:
- The mesoderm is one of the three primary germ layers in the early embryo (the other two being ectoderm and endoderm). It plays a crucial role in the development of various structures in animals.

2. **Analyzing Option A**:
- **Option A** states that the presence of mesoderm "restricts the development of a coelom."
- This statement is incorrect because the mesoderm is actually responsible for the formation of the coelom, which is a fluid-filled body cavity. Therefore, this option is not valid.

3. **Analyzing Option B**:
- **Option B** claims that the presence of mesoderm is "associated with the organ level of organization."
- This statement is correct. The mesoderm gives rise to various organs and systems, including the circulatory system, muscles, and skeletal structures, indicating its role in organ-level organization.

4. **Analyzing Option C**:
- **Option C** states that the presence of mesoderm is "associated with the development of muscles."
- This statement is also correct. The mesoderm differentiates into muscle tissue, making it essential for muscle development.

5. **Analyzing Option D**:
- **Option D** combines the previous two correct statements, stating that the presence of mesoderm is associated with both the organ level of organization (Option B) and the development of muscles (Option C).
- Since both B and C are correct, Option D is also correct.

6. **Conclusion**:
- The correct answer to the question about the presence of mesoderm is **Option D: both B and C**.

### Final Answer:
The presence of mesoderm is associated with the organ level of organization and the development of muscles. Therefore, the correct answer is **Option D: both B and C**.

---