1. Leucothrix niucor Oersted, 1844. (Oersted, De regionibus marinis, elementa topographiae historiconaturalis freti Oere- sund. J. C. Scharling, Copenhagen, 1844, 44; Chlamydothrix longissima Molisch, Cent, f. Bakt., II Abt., 33, 1912, 60; Pontothrix longissima Nadson and Krassilnikov, Compt. rend. Acad. Sci. de U.R.S.S., A. No. 1, 1932, 243; also see Harold and Stanier, Bact. Rev., 19, 1955, 49.) mu'cor. L. noun mucor mold; M.L. noun Mucor a genus of molds. Cells short, 1 to 5 microns long, cylindri- cal. Sulfur granules are found only on the exterior, never in the interior, of the cells, and they occur only when the trichomes lie near the surface of the water where there is an abundance of oxj'gen. Trichomes are colorless, unbranched, non-motile, occa- sionally surrounded by a gelatinous sheath 2 to 6 microns wide, and very long, fre- quently reaching a length of 0.5 cm or more; they are either entwined about each other or occur in loosely arranged bundles of sev- eral hundred or more where they lie parallel to each other or twist like the individual strands of a rope. The trichomes remain in contact with the surface film or with solid particles by means of an inconspicuous holdfast; in young colonics the trichomes radiate from the solid particles in a manner similar to that of Thiothrix sp. Reproduc- tion occurs by the fragmentation of the trichomes into gonidia. A large variety of carbohydrates and other simple organic compounds may serve as sources of carbon and energy. No growth factors are required. Strictly aerobic. Temperature relations: Optimum, 25° C. Maximum, 30° C. Grows best at a salt concentration (syn- thetic sea water) of 16 grams per liter; a salt concentration of 3 grams per liter sup- ports growth, but with abnormal morphol- ogy. Source: Isolated from decaying algal infusions. Found in the harbor at Trieste. Nadson and Krassilnikov (op. cit., 1932, 243) report this organism on Zostera marina in the Bay at Sebastopol on the Black Sea. Habitat: Found in fresh- and salt-water containing decomposing algal material. FAMILY IV. ACHROMATIACEAE MASSART, 1902.* (Rec. Inst. Bot., Univ. Bruxells, 5, 1902, 251.) A.chro.ma.ti.a'ce.ae. M.L. neut.n. Achromatium type genus of the family; -aceae ending to denote a family; M.L. fem.pl.n. Achromatiaceae the Achromatium family. Large, unicellular organisms which are spherical to ovoid or shortly cylindrical with hemispherical extremities. Movements, if any, are of a slow, rolling, jerky type and are dependent upon the presence of a substrate; no special organs of locomotion are known. Division of cells is by a constriction in the middle. Do not possess photosynthetic pigments. In their natural habitat, the cells contain sulfur droplets and sometimes additional in- clusions, such as large spherules of calcium carbonate. Found in fresh-water and marine environments. The organisms in the family Achromatiaceae have so far been studied exclusively as found in their natural habitats. Pure-culture studies are greatly needed; they may show that the peculiar calcium carbonate inclusions (not calcium oxalate as thought by Schewiakoff nor calcium thiosulfate as believed by Hannevart) occur only under special environmental conditions. There is a single genus, Achromatium Schewiakoff.
- Revised by Prof. C. B. van Niel, Hopkins Marine Station, Pacific Grove, California,
January, 1944; further revision, October, 1955.
