The Collaborative International Dictionary of English v.0.48:

Spirochaeta \Spi`ro*chae"ta\, Spirochaete \Spi`ro*chae"te\, n.
   [L. spira a coil + Gr. ??? hair.] (Biol.)
   A genus of Spirobacteria similar to Spirillum, but
   distinguished by its motility. One species, the Spirochaete
   Obermeyeri, is supposed to be the cause of relapsing fever.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Spirochaeta
    n 1: the type genus of the family Spirochaetaceae; a bacterium
         that is flexible, undulating, and chiefly aquatic [syn:
         Spirochaeta, genus Spirochaeta]