Final answer:
Tightly coiled spiral-shaped bacteria are called spirochetes, which are very thin and gram negative-like. They are different from other spiral bacteria like spirilla.
so the correct answer is C. spirochetes
Step-by-step explanation:
Tightly coiled spiral-shaped bacteria are called spirochetes. This bacterium shape is known for being very thin and often requires darkfield microscopy to be viewed adequately due to their gram negative-like properties. They differ from other spiral bacteria such as spirilla, which have a more rigid and less tightly coiled structure. Understanding the different shapes such as cocci (spherical), bacilli (rod-shaped), and spirilli (spiral-shaped) helps in the identification and classification of bacteria.
The correct answer to the question is C. spirochetes.