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In biological classification, class ((ラテン語:classis)) is: * a taxonomic rank. Other well-known ranks in descending order of size are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the prefix ''sub-'': subclass (Latin: ''subclassis''). * a taxonomic unit, a taxon, in that rank. In that case the plural is classes (Latin ''classes'') The composition of each class is determined by a taxonomist. Often there is no exact agreement, with different taxonomists taking different positions. There are no hard rules that a taxonomist needs to follow in describing a class, but for well-known animals there is likely to be consensus. For example, dogs are usually assigned to the phylum Chordata (animals with notochords); in the class Mammalia; in the order Carnivora. In botany, classes are now rarely discussed. Since the first publication of the APG system in 1998, which proposed a taxonomy of the flowering plants up to the level of orders, many sources have preferred to treat ranks higher than orders as informal clades. Where formal ranks have been assigned, the ranks have been reduced to a very much lower level, e.g. class Equisitopsida for the land plants, with the major divisions within the class assigned to subclasses and superorders. == Hierarchy of ranks == For some clades, a number of alternative classifications are used. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Class (biology)」の詳細全文を読む スポンサード リンク
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