[Highest level of division in classification of organisms. 3. Monodermata and Didermata].
The deepening our knowledge and embrassing the larger array of the investigated organisms leads to replacement of typological classifications with phylogenetic ones. This process seems to be the main stream of modern systematics. But typological classifications have not lost the value, remaining the important tool of the description of phylogeny. It is especially obvious today when molecular reconstructions are using so widely. However resulted phylogenetic classifications are difficult for understandable interpretation. Therefore phylogeneticist is interested in elaboration of typological classifications that can help to explain the results. As an example the phylogenetic classifications of organisms proposed recently by Cavalier-Smith (1998, 2002) and Gupta (1998, 2000) are considered. The modified system of Gupta is the most adequate description of organism phylogeny. Basal clostridia and togobacteria have to the greatest degree kept features of a common ancestor of organisms. From this common ancestor evolution spread by two phyletic lines. One of them included Gram-negative bacteria. The main groups of them have branched of from a common ancestor in the following order: (Deinococci, Chloroflexi) --> (Cyanobacteria) --> (Chlamydia, CFB, Fibrobacteria, Chlorobia) --> (Aquificae) --> --> (Epsilonproteobacteria, Deltaproteobacteria) --> (Alfaproteobacteria) --> (Betaproteobacteria) --> --> (Gammaproteobacteria). In other phyletic line the main groups were separated in the following order: (Thermotogae) --> (Clostridia, Fusobacteria) --> (Bacillae) --> (Actinobacteria). Exact position of archaebacteria and eukaryotes related to this line remains unclear. Typological division of organisms into Didermata and Monodermata (Gupta, 1998) corresponds to these two branches of a cladogram. The cell of the diderm organisms is covered with two membranes, plasmatic and outer. The cell of the monoderm organisms has only one plasmatic membrane. Development of the cellular organization at the earliest stages of evolution of a life went through use of non-lamellar (non-bilayer) lipids which could give a cell with one membrane (not two membranes as in the scenario of Cavalier-Smith (2001)). Membranes appeared at the earliest stages of the evolution of life. Therefore their distinction is quite logical to take as a principle the first typological division of organisms. At the same time the typological classifications considered beyond the framework of phylogenetics, have no independent value. Typological classifications do not give monothetic division into groups. Always there are exceptions. So, among Monodermata there are Gram-negative forms (Acidaminococcaceae, Syntrophomonadaceae, some Thermoanaerobacteriaceae), which are didermic.
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Shatalkin
D001419:Bacteria / Q000145:classification* / Q000166:cytology; D005075:Biological Evolution; D002462:Cell Membrane; D005057:Eukaryotic Cells / Q000145:classification / Q000166:cytology; D010802:Phylogeny