Final answer:
The spirochete is the type of bacterial cell with a flexible, spring-like structure containing periplasmic flagella enabling its unique corkscrew-like motility.
Step-by-step explanation:
The bacterial cell type that is described as a flexible, spring-like structure containing periplasmic flagella is a spirochete. These bacteria are unique in that their flagella are located in the periplasmic space between the inner and outer membranes of the cell, which gives them their distinctive spiral shape and allows them to move in a corkscrew-like manner. This arrangement is different from other types of bacteria that have flagella protruding outside the cell. The movement provided by these periplasmic flagella allows spirochetes to be highly motile in viscous environments.