Many bacteria are long but narrow. Some of the larger species are Schaudinnum butschlii, 50 to 60 micrometers long and 4 to 5 μm thick and Spirochaeta plicatilis, 250 μm long by 0.75 μm thick. A typical very large rounded bacterium, Achromatium oxaliferium is about 100 μm by 45 μm.In 1993, DNA testing revealed that Epulopiscium fishelsoni, an organism that only lives in the guts of a brown surgeonfish found in the Red Sea, is an extraordinary kind of bacteria. Individual specimens have been measured at 80 mm thick and more than 600 μm long (more than half a millimeter, making them visible to the naked eye). Similar species are found in the guts of surgeonfish on Australia's Great Barrier Reef. It had previously been assumed that prokaryotes were bound to be small because the materials could only travel through the cell by diffusion. (Eukaryotes have ways of actively transporting materials within the cell.) On this assumption, microfossils had been classified as eukaryotes solely because of their size.A sulfur bacteria found in sediments off the coast of Namibia in 1997, Thiomargarita namibiensis, is typically 0.1 to 0.3 millimeters in diameter, but some are almost half a millimeter wide and visible to the naked eye. Most of the cell volume is a vacuole of sulfur. The bacteria are frequently found in loosely bound chains.