Chloroflexus (cloe-row-flecks-us) is a filamentous green prokaryote, but not a cyanobacterium. It is common in some of the microbial mats which cover the sediments at some of the thermal sites. This image shows a mass of tightly intertwined cells. Phase contrast. Material provided by Mike Ferris from Mushroom Spring, a thermal site within Yellowstone National Park, photographs by Mike Ferris and David Patterson.