Source : WordNet®

spirilla
     n : any flagellated aerobic bacteria having a spirally twisted
         rodlike form [syn: {spirillum}]

spirillum
     n 1: spirally twisted elongate rodlike bacteria usually living in
          stagnant water
     2: any flagellated aerobic bacteria having a spirally twisted
        rodlike form [syn: {spirilla}]
     [also: {spirilla} (pl)]

spirilla
     See {spirillum}