A radially symmetrical diploblastic animal is

Options

A. (a) Round worm
B. (b) Earthworm
C. (c) Hydra
D. (d) Liver fluke

Answer

To solve the question "A radially symmetrical diploblastic animal is," we need to analyze the characteristics of the organisms listed in the options and determine which one fits the criteria of being radially symmetrical and diploblastic.

### Step-by-Step Solution:

1. **Understanding Radial Symmetry**:
- Radial symmetry means that the body can be divided into similar halves by multiple planes passing through the central axis. This is a primitive feature found in certain animal groups.

2. **Understanding Diploblastic Organisms**:
- Diploblastic organisms have two germ layers: the ectoderm (outer layer) and the endoderm (inner layer). They lack a mesoderm (middle layer), which is characteristic of triploblastic organisms.

3. **Identifying Relevant Phyla**:
- The two main phyla that exhibit radial symmetry and are diploblastic are:
- **Cnidaria** (e.g., jellyfish, corals, and hydra)
- **Porifera** (sponges)

4. **Evaluating the Options**:
- **Option A: Roundworm** - Roundworms belong to the phylum Nematoda, which are triploblastic and exhibit bilateral symmetry. This option is incorrect.
- **Option B: Earthworm** - Earthworms belong to the phylum Annelida, which are also triploblastic and exhibit bilateral symmetry. This option is incorrect.
- **Option C: Hydra** - Hydra belongs to the phylum Cnidaria, which is radially symmetrical and diploblastic. This option is correct.
- **Option D: Liver Fluke** - Liver flukes belong to the phylum Platyhelminthes (flatworms), which are triploblastic and exhibit bilateral symmetry. This option is incorrect.

5. **Conclusion**:
- After evaluating all the options, the only organism that is both radially symmetrical and diploblastic is **Hydra** from the phylum Cnidaria.

### Final Answer:
The correct answer is **C: Hydra**.