B. Diameter of trichomes is less than 0.5 micron. 3. Thiothrix tenuissima. II. From marine environments. A. Diameter of trichomes is greater than 15 microns. 4. Thiothrix voukii. B. Diameter of trichomes is less than 15 microns. 1. Diameter of trichomes is greater than 1.8 microns. a. Segments about 25 microns long. 5. Thiothrix longiarticulata. aa. Segments about 1 micron long. 6. Thiothrix anulata. 2. Diameter of trichomes is less than 1.8 microns. 7. Thiothrix marina. 1. Thiothrix nivea (Rabenhorst, 1865) Winogradsky, 1888. {Beggiatoa nivea Raben- horst, Flora europaea algarum, 2, 1865, 94; Winogradsky, Beitr. z. Morph. u. Physiol, d. Bact., I, Schwefelbacterien, 1888, 39.) ni've.a. L. adj. niveus snow-white. Trichomes, 2.0 to 3.0 microns at the base, 1.7 microns in the middle and 1.4 to 1.5 mi- crons at the tip, occurring within a thin sheath. Segmentation invisible as long as the trichomes contain sulfur globules; the segments measure 4 to 15 microns, the longer ones usually near the apex, the shorter ones near the base. Motile segments (so-called conidia) are mostly single, 8 to 15 microns long, sometimes occurring in short tri- chomes of 2 to 4 cells and measuring up to 40 microns long. These segments may settle and develop near the base of the parent trichome or on a trichome itself, forming verticillate structures. Habitat: Found in fresh-water environ- ments where hydrogen sulfide is present (sulfur springs, stagnant pools, submerged decaying vegetation, etc.). 2. Thiothrix tenuis Winogradsky, 1888. {Beggiatoa alba var. uniserialis Engler, tJber die Pilz-Vegetation des weissen oder todten Grundes in der Kieler Bucht. Vierter Be- richt der Commission zur wissenschaft- lichen Untersuchung der deutschen Meere in Kiel fiir 1877 bis 1881, Abt. I, 1883, 187- 193; Winogradsky, Beitr. z. Morph. u. Phys- iol, d. Bact., I, Schwefelbacterien, 1888, 40.) te'nu.is. L. adj. tenuis slender. Trichomes, about 1 micron in diameter, of nearly uniform width, often occurring in dense, felted masses. Segments 4 to 5 mi- crons long. Habitat: Found in fresh-water environ- ments where hydrogen sulfide occurs. Also found in sea water, according to Baven- damm (Die farblosen und roten Schwefel- bacterien, Pflanzenforschung, Heft 2, 1924, 107). 3. Thiothrix tenuissima Winogradsky, 1888. (Beitr. z. Morph. u. Physiol, d. Bact., I, Schwefelbacterien, 1888, 40.) te.nu.is'si.ma. L. sup. adj. tenuissimus very slender. Trichomes less than 0.5 micron in diame- ter, usually occurring in dense masses. Habitat: Found in fresh-water environ- ments where hydrogen sulfide occurs. 4. Thiothrix voukii Klas, 1936. (Arch. f. Protistenk., 88, 1936, 123.) vou'ki.i. M.L. gen. noun voukii of Vouk; named for Vouk, a Yugoslavian scientist. Trichomes, 15 to 30, most frequently 17, microns in diameter, of rather uniform width. Segments visible without special treatment. Segments generally somewhat longer than wide, occasionally barrel- shaped, rarely square. Segments 15 to 30, mostly 19 to 23, microns in length. Motile segments not yet observed. Comment : Apart from the lack of motil- ity, this species closely resembles the motile Beggiatoa mirabilis. Source: Described from the effluent of sulfur springs at the seashore near Split, Yugoslavia. So far reported only once. Habitat: Found in marine environments containing hydrogen sulfide.
