Spirochaetes is/are a class of viruses, myxobacteria, spiral-shaped bacteria, or rickettsia?

Spirochaetes are highly motile bacteria which are primarily visualized by dark field microscopy. They are thin, spiral shaped or wave like bacteria which display classic corkscrew like motility due to presence of a periplasmic flagella. They are associated with syphilis (Treponema pallidum) and Lymes disease (Borellia burgdorferi) primarily.