Which of the following organisms is not radially symmetrical ?

Options

A. Pila
B. Echinus
C. Cucumaria
D. Ctenoplane

Answer

To determine which of the following organisms is not radially symmetrical, we will analyze each option provided:

1. **Understanding Radial Symmetry**:
- Radial symmetry means that an organism can be divided into similar halves by passing a plane through its center in multiple directions. Organisms with radial symmetry typically have a circular body plan.

2. **Analyzing the Options**:
- **Option 1: Pila** (a type of freshwater snail):
- Pila belongs to the phylum Mollusca. Mollusks, including snails, exhibit bilateral symmetry rather than radial symmetry. This means they can only be divided into mirror-image halves along one plane.
- **Option 2: Achenus** (a type of echinoderm):
- Achenus belongs to the phylum Echinodermata, which typically exhibits radial symmetry, especially in their adult forms.
- **Option 3: Cucumeria** (a type of sea cucumber):
- Cucumeria is also part of Echinodermata and exhibits radial symmetry.
- **Option 4: Cetanoplane** (another echinoderm):
- Cetanoplane also belongs to Echinodermata and displays radial symmetry.

3. **Conclusion**:
- After analyzing all the options, we conclude that the organism that is not radially symmetrical is **Pila** (Option 1), as it exhibits bilateral symmetry.

**Final Answer**: Pila (Option 1) is not radially symmetrical.

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