Most people still conceive different types of biological taxa and place them in ranks: some taxa are species, others are genera, while others are families. Linnaeus gave us his ranks in 1731. Although biological theory has changed since Linnaeus' time, the vast majority of biologists still assign Linnaean ranks to taxa, even though the practice is at odds with evolutionary theory and even though it causes a number of practical problems. Some authors abandon Linnaean ranks and propose alternative methods for displaying the hierarchical relations of taxa.
Whatever the view on this it must be remembered that ranking is a subjective decision. This explains why taxa may be ranked differently by different authors.
Links: http://en.wikiped...zoology%29, following the taxa link to related topics.
Round brackets are used to indicate that a species is currently placed in a genus different to the one in which it was originally described . For example: Liriomyza amoena (Meigen, 1830). Meigen (1830) originally descriped this species as Agromyza amoena. Nowadays it is placed in the genus Liriomyza Mik, 1894. Hence, 'Meigen, 1830' is placed in round brackets. Sometimes the original placement is given, thus Liriomyza amoena (Meigen, 1830: Agromyza).