**Core Concept**
Actinomyces are a group of Gram-positive, facultatively anaerobic bacteria that belong to the family Actinomycetaceae. Unlike typical bacteria, Actinomyces have a unique cell wall structure and exhibit a characteristic branching filamentous morphology.

**Why the Correct Answer is Right**
The key difference between Actinomyces and bacteria lies in their cell wall composition. Actinomyces have a thick, polysaccharide-rich cell wall that is resistant to lysozyme, an enzyme that breaks down peptidoglycan in bacterial cell walls. This unique cell wall structure allows Actinomyces to survive in environments with low oxygen levels and to adhere to host tissues. Actinomyces also have a distinctive branching filamentous morphology, which is in contrast to the rod-shaped or coccoid morphology of typical bacteria.

**Why Each Wrong Option is Incorrect**
**Option A:** Actinomyces are aerobic bacteria. **Incorrect**, as Actinomyces are facultatively anaerobic, meaning they can grow in both aerobic and anaerobic conditions.

**Option B:** Actinomyces have a peptidoglycan-rich cell wall. **Incorrect**, as Actinomyces have a polysaccharide-rich cell wall, not a peptidoglycan-rich one.

**Option C:** Actinomyces are obligate anaerobes. **Incorrect**, as Actinomyces are facultatively anaerobic, meaning they can grow in both aerobic and anaerobic conditions.

**Clinical Pearl / High-Yield Fact**
Actinomyces are commonly found in the human oral cavity and gastrointestinal tract, where they play a role in the breakdown of complex carbohydrates. However, they can also cause disease when they infect compromised tissues, such as in cases of actinomycosis.

**Correct Answer:** D.