Final answer:
Bacillus anthracis forms Medusa-head colonies on blood agar, which are distinguishable from other options provided due to its unique texture and pattern.
Step-by-step explanation:
The organism that looks like Medusa-head colonies is Bacillus anthracis. Bacillus anthracis is known to form colonies on blood agar with a rough texture and serrated edges that resemble a head of Medusa due to their undulating pattern. Other bacteria provided as options do not form these characteristic Medusa head patterns on agar plates. For instance,
Streptococcus pneumoniae shows other features such as lysis of red blood cells on blood agar and a characteristic lancet-shaped morphology, which differentiates it from B. anthracis.