Concept:
Bacteria are classified into different groups according to their shape.
The common bacterial shapes are:
• Coccus – Spherical
• Bacillus – Rod-shaped
• Vibrio – Comma-shaped
• Spirillum – Spiral-shaped
Step 1: Identify the shape of each bacterial type.
The characteristic shapes are:
\[
\boxed{\text{Coccus} \rightarrow \text{Spherical}}
\]
\[
\boxed{\text{Bacillus} \rightarrow \text{Rod-shaped}}
\]
\[
\boxed{\text{Vibrio} \rightarrow \text{Comma-shaped}}
\]
\[
\boxed{\text{Spirillum} \rightarrow \text{Spiral-shaped}}
\]
Step 2: Compare the given options.
Option (A) is incorrect because coccus is spherical.
Option (B) is incorrect because bacillus is rod-shaped.
Option (C) correctly states that spirillum is spiral-shaped.
Option (D) is incorrect because vibrio is comma-shaped.
Step 3: Choose the correct option.
Thus,
\[
\boxed{\textbf{Option (C)}}
\]
is the correct answer.