While moving along the bank of a river you notice an organism that creeps that over the surface of mud. It has a protective shell which covers the entire body and a muscular foot for locomotion. Assign the organism to its appropriate phylum.

Answer

**Step-by-Step Solution:**

1. **Observation of the Organism**: The organism in question is observed to be creeping over the surface of mud along the riverbank.

2. **Identification of Key Features**: The organism has two notable features:
- A protective shell that covers its entire body.
- A muscular foot that aids in locomotion.

3. **Comparison with Known Organisms**: Based on the features described, we can compare this organism with known classifications in biology. The presence of a shell and a muscular foot suggests that it is likely a mollusk.

4. **Classification of the Organism**: The organism is identified as a snail, which is a common example of a mollusk.

5. **Phylum Assignment**: Given that snails are soft-bodied organisms with a protective shell, they are classified under the phylum **Mollusca**.

**Final Answer**: The organism belongs to the phylum **Mollusca**.

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