**Core Concept**
Genus Neisseria includes two important pathogenic species, Neisseria meningitidis and Neisseria gonorrhoeae, which cause meningitis and gonorrhea, respectively. These bacteria are characterized by their unique morphology and Gram staining properties.

**Why the Correct Answer is Right**
Neisseria species are Gram-negative diplococci, meaning they have a thin peptidoglycan cell wall and an outer membrane containing lipopolysaccharides. This Gram-negative staining pattern is a result of the presence of an outer membrane, which is not present in Gram-positive bacteria. The diplococci morphology of Neisseria species refers to their paired coccoid cells, which are typically seen in clinical specimens. This distinctive morphology is a key feature for identifying Neisseria species.

**Why Each Wrong Option is Incorrect**
**Option A:** Gram-positive diplococci are not characteristic of Neisseria species. Gram-positive bacteria have a thick peptidoglycan cell wall, which is not present in Neisseria.
**Option C:** Gram-negative coccobacilli are not a characteristic morphology of Neisseria species. While some Gram-negative bacteria can have a coccobacillary shape, Neisseria species are typically diplococci.
**Option D:** Gram-positive bacilli are not a characteristic of Neisseria species. Bacillary morphology is not typically associated with Neisseria, which are coccoid in shape.

**Clinical Pearl / High-Yield Fact**
To remember the distinctive morphology of Neisseria species, recall that they are "diplo-cocci" (meaning paired coccoid cells), which is a key feature for identifying these bacteria in clinical specimens.

**✓ Correct Answer: B. Gram negative diplococci**