Mesoglea occurs between
(a) Ectoderm and endoderm
(b) Ectoderm and mesoderm
(c) Mesoderm and endoderm
(d) Just below mesoderm.

Options

A. Ectoderm and endoderm
B. Ectoderm and mesoderm
C. Mesoderm and endoderm
D. Just below mesoderm.

Answer

To solve the question regarding the occurrence of mesoglea, we can follow these steps:

### Step 1: Understand the Definition of Mesoglea
Mesoglea is a gelatinous substance found in certain organisms, particularly in cnidarians (like jellyfish, corals, and sea anemones) and sponges. It acts as a non-living layer that separates the two main cell layers in these organisms.

### Step 2: Identify the Cell Layers in Cnidarians
Cnidarians have two primary layers of cells:
- **Ectoderm**: The outer layer of cells.
- **Endoderm**: The inner layer of cells.

### Step 3: Determine the Position of Mesoglea
Mesoglea is located between the ectoderm and the endoderm. It is important to note that mesoglea is not a true tissue layer like mesoderm; instead, it is a non-living layer that provides structural support.

### Step 4: Analyze the Options
Now, let's analyze the provided options:
- (a) Ectoderm and endoderm: This is the correct answer, as mesoglea is indeed found between these two layers.
- (b) Ectoderm and mesoderm: This is incorrect; mesoderm is not present in cnidarians.
- (c) Mesoderm and endoderm: This is incorrect for the same reason as option (b).
- (d) Just below mesoderm: This is also incorrect, as mesoglea does not exist below mesoderm in cnidarians.

### Conclusion
Based on the understanding of mesoglea and the structure of cnidarians, the correct answer is:
**(a) Ectoderm and endoderm.**

---