Biradial symmetry and lack of cnidoblasts are the characteristics of

Options

A. Hydra and starfishes
B. Starfish and sea anemone
C. Ctenophore and Beroe
D. Aurelia and paramoecium

Answer

To solve the question regarding the characteristics of biradial symmetry and the lack of cnidoblasts, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Terms**:
- **Biradial Symmetry**: This is a type of symmetry where the body can be divided into similar halves in two different planes. It is typically found in certain marine organisms.
- **Cnidoblasts**: These are specialized cells found in cnidarians (like jellyfish, corals, and sea anemones) that contain stinging structures called nematocysts. The absence of these cells indicates that the organism does not belong to the phylum Cnidaria.

2. **Identifying the Organisms**:
- We need to analyze the options provided:
- a. Hydra and starfishes
- b. Starfish and sea anemones
- c. Ctenophore and Beroe
- d. Aurelia and Paramecium

3. **Analyzing Each Option**:
- **Option a (Hydra and starfishes)**: Hydra is a cnidarian and has cnidoblasts. Starfishes (echinoderms) do not exhibit biradial symmetry.
- **Option b (Starfish and sea anemones)**: Sea anemones are cnidarians and have cnidoblasts. Starfish do not exhibit biradial symmetry.
- **Option c (Ctenophore and Beroe)**: Ctenophores (like Beroe) exhibit biradial symmetry and lack cnidoblasts. This option fits the criteria.
- **Option d (Aurelia and Paramecium)**: Aurelia is a jellyfish (cnidarian) and has cnidoblasts. Paramecium is a protozoan and does not exhibit biradial symmetry.

4. **Conclusion**:
- The only option that fits both characteristics of biradial symmetry and the absence of cnidoblasts is **Option c (Ctenophore and Beroe)**.

### Final Answer:
**Option C: Ctenophore and Beroe**