spirilla n any flagellated aerobic bacteria having a spirally twisted rodlike form n spirally twisted elongate rodlike bacteria usually living in stagnant water n any flagellated aerobic bacteria having a spirally twisted rodlike form Usage(s) Bacteria are divided into three groups, the cocci (spherical or berry-shaped), the bacilli (elongated or rod-shaped), the spirilla (twisted or spiral-shaped). Synonym(s) spirillum