Biradial symmetry and lack of cnidoblasts are the characteristics of

Options

A. Hydra and aurelia
B. Aurelia and adamsia
C. Ctenoplana and pleurobrachia
D. Aurelia and Paramoecium

Explanation

To determine which organism exhibits biradial symmetry and lacks cnidoblasts, we can follow these steps:

### Step 1: Understanding Symmetry Types
- **Biradial Symmetry**: This is a combination of bilateral and radial symmetry. In biradial symmetry, body parts are arranged symmetrically around a central axis, but only in certain planes.
- **Cnidoblasts**: These are specialized cells found in cnidarians (like jellyfish and corals) that contain stinging structures called nematocysts. Organisms lacking cnidoblasts do not possess these stinging cells.

### Step 2: Identifying Relevant Organisms
- The question provides several options: Hydraurea, Aurelia, Dentsia, Tenoplana, and Pleurobranchia.
- **Aurelia** is a genus of jellyfish, which are cnidarians and thus possess cnidoblasts.
- **Hydraurea** and **Dentsia** are also cnidarians and would have cnidoblasts.
- **Tenoplana** and **Pleurobranchia** belong to the phylum Ctenophora (comb jellies), which are known for having biradial symmetry and lack cnidoblasts.

### Step 3: Conclusion
- Based on the characteristics of biradial symmetry and the absence of cnidoblasts, the correct answer is **Tenoplana** or **Pleurobranchia** from the phylum Ctenophora.

### Final Answer
The characteristics of biradial symmetry and lack of cnidoblasts are exhibited by **Tenoplana** or **Pleurobranchia**.

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