The Living World Test 8

Classification is the arrangement of organisms into convenient categories or orouos on the basis of their similarities and differences in certain easily observable but tundamental characters. A hierarchy of categories is raised keeping in mind the affinities or relationships of various groups. The various taxonomic categories represent distinct biological entities and not merely morphological aggregates.
The various categories are kingdom, phylum (or division in plants), class, order, family, genus and species.

Hierarchy of categories is the classification of organisms in a definite sequence of categories (taxonomic categories) in a descending order starting from kingdom and reaching upto species or an ascending order from species to kingdom. The number of similar characters of categories decreases from lowest rank (species) to highest rank (kingdom). The taxonomic hierarchy includes seven obligate categorieskingdom, division or phylum, class, order, family, genus and species.

From the given representation of taxonomical hierarchy, it is clear that family is interpolated between order and genus. Some subcategories like tribe, subfamily, subspecies are also used whenever required.

The number of similar characters of categories decreases - from lowest rank to highest rank in a taxonomic hierarchy. Out of the given categories i.e. family, class, genus and species, the class being the highest category possesses the least similar characters.

Given plant is Helianthus sp. which can be classified as:
Kingdom - Plantae
Division - Angiospermae
Class - Dicotyledonae
Order - Asterales
Family - Compositae (= Asteraceae)
Genus - Helianthus

Species occupies a key position in classification and it represents the lowest taxonomic category. As per the definition given by Ernst Mayr in 1964 :
"A species is a group of actually or potentially inbreeding populations that are reproductively isolated from other such groups.''
A species may have subgroups, called subspecies or varieties, showing certain distinct features of their own.

Family is a taxonomic category which contains one or more related genera. All the genera of a family have some common features and they are separable from genera of a related family by important characteristic differences. The family Solanaceae includes a number of genera like Solanum, Petunia, Atropa, etc. due to certain similarities. They are distinct from the genera of the related family Convolvulaceae such as Convolvulus, Ipomoea. In the same way, the family Felidae which includes the genus Panthera of lion, tiger, leopard and genus Felis of cats is distinctly separated from the family Canidae which includes dogs and foxes.

Musca domestica (Housefly) belongs to class-lnsecta of phylum- Arthropoda.

The class-Aves (or Birds) belongs to kingdom-Animalia and phylum-Chordata.

Taxon is a unit of classification which may represent any level of grouping of organisms based on certain easily observable common characteristics. May (1964) has defined taxon to be a taxonomic group of any rank that is sufficiently distinct to be worthy of being assigned to a definite category.

Tautonyms are the scie ntific names in which both generic and specific epithets are same. Tautonyms are used in zoological nomenclature. However, in the current rules for nomenclature of living organisms, tautonyms are explicitly prohibited. Examples of tautonyms are Rattus rattus (Rat), Catla catla (Catla), Gorilla gorilla (Western gorilla), etc.

Order includes one or more related families e.g. the family Solanaceae is placed in the order Polemoniales along with four related families (Convolvulaceae, Boraginaceae, Hydrophyllaceae and Polemoniaceae). Name of a plant order usually ends with 'ales'.

Phylum Arthropoda is the largest phylum of kingdom Animalia. It includes the largest number of animals with about 900,000 species. Phylum Mollusca is the second largest animal phylum, which includes over 60,000 species.

Euplectella (The Venus' flower basket) belongs to phylum Porifera (5ponges). It is found in deep sea water. Its skeleton is given as a costly marriage gift in Japan as it is thought to be a symbol of union of wife and husband.

sapiens, americana and rotundus are the specific names whereas Hemidactylus (wall lizard or Gecko) is the generic name.

According to ICBN, the names of different categories must end in the standard suffixes for plants as gives below:
Category -  Sulfix
Division  -    phyta
Sub-division  -  phytina
Class    -     phyceae or opsida or ae
Order    -      ales
Sub-order  -  incae
Family    -     aceae
Sub-family  -  oideae
Tribe    -      eae
Suffixes used in animal kingdom are:
Super family - oidea
Family - idae
Sub family - inae
Tribe - ini
Tribe is an intermediate category between sub-family and genus.