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Dunal (1837) originally described the taxon now known asDunaliella salina(Dunal) Teodoresco, 1905, as consisting of spherical or elliptical cells, red-orange to rust coloured. Teodoresco, in his definition of the species (1905) stated that the zoospores had a green chromatophore but in aged zoospores the entire body, including chromatophore, was red. Thus, by definition, any isolate ofDunaliellawhich is not capable of turning redorange to rust coloured should not be consideredD. salina. Several strains have been reported in the literature under the nameD. salinabut do not meet the aforementioned criteria. These include UTEX 200 (= Cambridge 19/3), Mil'ko's strain (Mil'ko, 1963a, b) and Strain No. 6 used by Mironyuk (Drokova, 1970; Drokova, Popova & Tupik, 1964; Drokova & Popova, 1973, 1974; Mironyuk 1969a, b; Mironyuk & Einor, 1968).

The organism Methanobacterium thermoautotrophicum, an archaebacterium, is envolutionarily very distant from both traditional prokaryotes and eukaryotes. Its genome (DNA) has physical characteristics typical of most prokaryotes except that it is quite small (about 10(9) daltons, less than half the size of the genome of Escherichia coli) and contains a significant amount (6 percent) DNA which renatures extremely rapidly.

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