Spirochaetes (also spelled spirochetes) belong to a phylum of distinctive diderm (double-membrane) bacteria, most of which have long, helically coiled (corkscrew-shaped or spiraled,hence the name) cells. Spirochaetes are chemoheterotrophic in nature, with lengths between 5 and 250 µm and diameters around 0.1–0.6 µm.