Answer:
The correct answer is- spirochetes
Explanation:
Spirochetes are a group of bacteria which are long, flexible and helical shaped. Some of them are associated with some disease in humans like yawns, lime disease, syphilis, etc.
Yawn is childhood infectious disease caused by a spirochete bacteria called Treponema pallidum pertenue. These bacterial usually affect the children who live in tropical regions like Africa, Southeast Asia. They can affect skin, bones, and joints. They can spread through direct contact with skin sores.
So the cells of T. pertenue which are helical, relatively long, and flexible known as spirochetes.