Shell is absent in

Options

A. Pila
B. Sepia
C. Octopus
D. Clams, mussels and oysters

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for an organism that does not have a shell. This is a specific feature we need to identify within the context of the animal kingdom, particularly focusing on the phylum Mollusca.

2. **Phylum Mollusca Overview**: Mollusca is a diverse phylum that typically includes organisms with shells. Most members of this phylum possess a shell, which serves as a protective structure.

3. **Identifying Exceptions**: Within the phylum Mollusca, there are exceptions where certain classes or species do not have shells. One notable class is Cephalopoda.

4. **Cephalopoda Class**: This class includes organisms such as squids, octopuses, and cuttlefish. Among these, the octopus is a key example of a mollusk that lacks a shell.

5. **Characteristics of Octopus**: The octopus is a soft-bodied animal, meaning it does not have a hard external shell or skeleton. This distinguishes it from other mollusks that typically have shells made of calcium carbonate.

6. **Conclusion**: Based on the information gathered, the organism that is known to be shell-less within the phylum Mollusca is the octopus. Therefore, the correct answer to the question is "Octopus."