**Core Concept**
The key difference between anthrax bacilli (*Bacillus anthracis*) and anthracoid bacilli lies in their **morphological** and **biochemical properties**. *Bacillus anthracis* is the causative agent of **anthrax**, a severe infectious disease.

**Why the Correct Answer is Right**
Anthrax bacilli are distinguished by their **polysaccharide capsule**, which is composed of **D-glutamic acid**, and their lack of **motility**. This capsule is a critical **virulence factor** that prevents phagocytosis by the host's immune cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the presence of a capsule is a key distinguishing feature.
**Option B:** Incorrect as anthracoid bacilli may also have similar growth requirements.
**Option C:** Incorrect because it does not specifically differentiate *Bacillus anthracis* from anthracoid bacilli.
**Option D:** Incorrect as the absence of motility is indeed a characteristic of *Bacillus anthracis*.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that *Bacillus anthracis* is **non-motile**, which is a critical feature for its identification.

**Correct Answer:** D. Non-motile.