**Core Concept**
Non-motile organisms are those that do not possess the ability to move or exhibit movement on their own. This characteristic is often contrasted with motile organisms, which can move using various mechanisms such as flagella, cilia, or pseudopodia. In microbiology, non-motility is an important characteristic for identifying and classifying microorganisms.

**Why the Correct Answer is Right**
The correct answer is likely *Bacillus anthracis*, a Gram-positive, non-motile bacterium. Bacillus anthracis lacks the flagella necessary for movement, which is a key feature of its identification. This is due to the absence of the *flaA* gene, which encodes for flagellin, the protein subunit of flagella. As a result, B. anthracis is unable to exhibit motility on agar plates, making it a non-motile organism.

**Why Each Wrong Option is Incorrect**
**Option A:** *Escherichia coli* is a Gram-negative, motile bacterium that exhibits flagellar movement. It is a common inhabitant of the human gut and is known for its ability to move using peritrichous flagella.

**Option C:** *Staphylococcus aureus* is a Gram-positive, motile bacterium that exhibits a "rabbit ear" or "dumbbell" shape under the microscope. It is known for its ability to form biofilms and cause a range of infections.

**Clinical Pearl / High-Yield Fact**
Non-motility is an important characteristic for identifying and classifying microorganisms, particularly in the context of laboratory diagnosis. It can be used to distinguish between different species of bacteria, and is often used in conjunction with other characteristics such as Gram stain and biochemical tests.

**Correct Answer: B. Bacillus anthracis**