Which of the following is diploblastic
(a) Fasciola
(b) Pheretima
(c) Palaemon
(d) Hydra

Options

A. Fasciola
B. Pheretima
C. Palaemon
D. Hydra.

Answer

To determine which of the given organisms is diploblastic, we need to understand the concept of germ layers in animals. Here’s a step-by-step solution:

### Step 1: Understand Diploblastic Organisms
Diploblastic organisms are those that have two primary germ layers:
- **Ectoderm**: The outer layer.
- **Endoderm**: The inner layer.

### Step 2: Identify the Germ Layer Composition of Each Organism
Now, let's analyze the options provided:

- **(a) Fasciola**: This is a genus of parasitic flatworms, commonly known as liver flukes. They are triploblastic, meaning they have three germ layers: ectoderm, mesoderm, and endoderm.

- **(b) Pheretima**: This is a genus of earthworms. Like Fasciola, Pheretima is also triploblastic, possessing ectoderm, mesoderm, and endoderm.

- **(c) Palaemon**: This is a genus of shrimp. Palaemon is also triploblastic, having the same three germ layers: ectoderm, mesoderm, and endoderm.

- **(d) Hydra**: Hydra is a genus of small, freshwater organisms belonging to the phylum Cnidaria. They are diploblastic, having only ectoderm and endoderm.

### Step 3: Conclusion
After analyzing the germ layer composition of each organism, we conclude that:
- **Hydra** is the only organism listed that is diploblastic.

### Final Answer
The correct answer is **(d) Hydra**.

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