**Core Concept**
Shigella and E. coli are both Gram-negative, rod-shaped bacteria, but they belong to different genera. Shigella is a member of the Enterobacteriaceae family, while E. coli is also a member of the same family. However, Shigella is non-motile and lacks the flagellar apparatus, whereas E. coli is motile.

**Why the Correct Answer is Right**
Shigella can be differentiated from E. coli by its lack of motility and flagella, which is due to the absence of the flagellar apparatus. This is a result of the loss of the fliC gene in Shigella, which codes for the flagellin protein. Additionally, Shigella is generally smaller in size than E. coli and has a more rounded shape.

**Why Each Wrong Option is Incorrect**
**Option A:** This feature is not unique to Shigella, as some strains of E. coli can also be non-motile.
**Option B:** While Shigella is indeed more resistant to desiccation than E. coli, this is not the most distinctive feature that differentiates the two bacteria.
**Option C:** This feature is characteristic of Shigella, as it is unable to ferment lactose, unlike most E. coli strains.

**Clinical Pearl / High-Yield Fact**
When differentiating between Shigella and E. coli, remember that Shigella is non-motile and lacks the ability to ferment lactose. This is due to the loss of the flagellar apparatus and the fliC gene.

**Correct Answer:** A. This feature is not unique to Shigella, as some strains of E. coli can also be non-motile.