Principles of animal Classifiation: Taxonomic Hierarchy, Animal Nomenclature, Law of Priority, Documentation, Necessity of Animal Classification

Introduction:

In the world, there are about 8.7 million species, and the variety among them is astounding. In addition, no two members of any animal form are identical. In order to study the animal world, some arrangements must be made to group them into sensible categories. The diversity or differences also show how similar different organisms are to one another.

Of the 8.7 million species, 6.5 million are land-based and 2.2 million are found in oceans and other bodies of water. Of the estimated 8.7 million species, zoologists predict that only 15% have been linked to humans.  The Animal Kingdom only has 953 434 animal species listed in its catalog.

Here are The main basic principles of classification mentioned below:

(A) Taxonomic Categories: principles

When classifying animals into different levels or placed in steps. These levels or steps are called hierarchical levels or steps or categories. Animals that are included in different steps or levels for classification purposes are called taxa (plural - taxa). That is, a group of people at any level of classification is called a taxon. A taxon is a taxonomic unit. Each category of the population used in classification is called a taxon. Examples:  Animalia, Chordata, Mammalia, Primates, Hominidae, and Homo are each taxon. Various steps introduced by Linnaeus with some modifications are used for the classification of animals.

The main units of classification are 7. Their order is as follows:

       Units Symbol

1. Kingdom     K

2. Phylum     P

3. Class    C

4. Order    O

5. Family    F

6. Genus    G

7. Species    Sp

Let's try to briefly define the main seven units of classification.

1. Species: Species is the lowest and most functional unit of classification of organisms. Species refers to a group of organisms that are geographically and ecologically separated but capable of producing fertile offspring through sexual intercourse. For example, one species of pigeon is Columba livia .

2. Genus: A genus consists of several related species. Chromosome number, size, shape, type, etc. play a role in determining fate. Its characteristics are related to adaptation. A species of the organism may spread over one or more regions. For example, Columba is a genus of pigeons.

3. Family:  A family is made up of several interrelated clans. Its spread is worldwide. For example, humans belong to the family Hominidae 

4. Order: Order consists of several interrelated groups. Its spread is worldwide. For example: Guinea pig belongs to the Rodentia class.

5. Class:  A class is made up of several interrelated classes. Classification of animals depends. On morphological features of the body, adaptive features, expressive style, etc. For example, humans belong to the class Mammalia.

6. Phylum: Phylum consists of several interrelated classes. It is the largest unit of classification. In the classification of animals, one phase is separated from another by obvious differences. E.g. Guinea pig belongs to the order Chordata.

7. Kingdom: The highest unit of the hierarchy of organisms is the kingdom. In this step of animal classification. All animals on earth are included in this unit.

                                                         Figure: The taxonomic hierarchy

The taxonomic hierarchy and taxa with 7 categories of humans are as follows:

         Category Taxon

1. Kingdom Animalia

2. Phylum Chordata

3. Class Mammalia

4. Order Primates

5. Family Homonidae

6. Genus Homo

7. Species Homo sapiens

Carolus Linnaeus introduced this seven-tier hierarchical structure of the hierarchy is called Linnaean Hierarchy. According to the nomenclature, the main units or levels of classification are seven. Units can be increased if needed. If a new unit is needed above or below a main unit, add super before the main unit and sub after it. For example – the superclass

Subclass Simpson (1961) introduced a hierarchy with 21 categories or levels. 

The modern hierarchy given by Scientist Simpson is as follows-

1. Kingdom. 

2. Phylum.

3. Sub-Phylum. 

4. Super Class. 

5. Class.

6. Sub-Class.

7. Infra Class.

8. Cohort. 

9. Super Order.

10. Order.

11. Sub-Order.

12. Infra Order.

13. Super Family. 

14. Family.

15. Sub-Family. 

16. Tribe.

17, Sub-Tribe.

18. Genus. 

19. Sub-Genus.

20. Species.

21. SubSpecies.

B. Species and Subspecies:

Species: 

The lowest level and basic unit of animal classification are species. John Ray (1986) first uses the word Species. Two definitions of species are mentioned here- 

(1) A species is a group of natural organisms having the most common characteristics, which produce fertile offspring among themselves through sexual reproduction. 

(2) A species is a set of organisms capable of interbreeding in a natural surroundings, which are derived from other organisms.

Subspecies: 

Distinct organisms or populations of genes from each other capable of interbreeding are called subspecies of the same species. Formerly considered a subspecies variety would have been as the subspecies differ in appearance, there is no difficulty in identifying them. Generally, Subspecies are groups of organisms that live in separate geographic areas, and in that case, the geographic areas are collectively included in the range of the species. 

(C) Animal Nomenclature: 

There are thousands of animals in the world. An animal is called by different names in different languages in different countries of the world. It causes complications in scientific research. To overcome this problem scientific method of animal naming has been introduced. Nomenclature is the special name given to each species of the animal according to certain rules and methods of classification (scientific method) for identifying a particular animal. The naming of animals is of two types viz.

(1) Binomial Nomenclature: 

According to the international convention of Nomenclature of Organisms, the naming of animals using first the genus name and then the species name is called binomial nomenclature. Swedish taxonomist Carolus Linnaeus introduced binomial nomenclature in 1758 AD. According to binomial nomenclature, the scientific name for humans is Homo sapiens L, where L stands for the species name Homo sapiens and L is the initial for the Linnaeus name.

(2) Tri-nominal Nomenclature: 

The nomenclature of organisms using three terms of species and sub-species is called tri-nominal nomenclature. Animal subspecies are named according to the tripartite nomenclature. For example, the scientific name of the Gokra snake is Naja najas, which has two subspecies - Naja naja naja (Gokra) and Naja naja hannah (Jati snake). German ornithologist Hermann Schlegel (1844) was the first to introduce the tripartite nomenclature of animals. The tripartite nomenclature is recognized by the ICZN.

Rules of Nomenclature: 

Scientist Carolus Linnaeus (1753) first introduced the concept of binomial nomenclature in his book Species Plantarum and later formulated the rules of binomial nomenclature in his book Systema Naturae, tenth edition (1758). Animal nomenclature rules are formulated by ICZN (International Commission on Zoological Nomenclature) and these rules are recorded in ICZN (International Code of Zoological Nomenclature). Following are some rules for naming animals by ICZN (International Commission on Zoological Nomenclature). 

                                                               Figure: Carolus Linnaeus

1. Each animal will have a specific scientific name, never the same name for two animals or two names cannot be used on an animal.

2. The scientific name of the animal will consist of two parts (in binomial nomenclature) or three parts (in the case of trinomial nomenclature). For these parts, the first part indicates the genus, the second part the species and the third part indicates the subspecies. 

3. Scientific names of animals must be Latin or Latinized. 

4. The plural part of a binomial noun is a noun whose first letter is a capital letter and the specific part is the adjective (adjective) of which all parts including the first letter must be written in English small letters For example - Homo sapiens.

5. Scientific names should always be written in italics type (curved to the right) in printed letters. For example- Homo sapiens.

6. The first published scientific name in an international scientific journal will be recognized.

7. While writing by hand, separate marks should be made under the name of the genus and species. For example - Homo sapiens (note, even if only the name of the genus is written, it should be underlined. For example – Homo. 

8. The scientist who gives the first scientific description of an organism, his name, and the year of publication will be added at the end of the scientific name of the organism. For example - Homo sapiens Linnaeus, 1758.

9. If a living entity has more than one name or if more than one living entity has the same name, the correct name is given first will be accepted. This is called the law of priority. In this case, any name prior to the tenth edition (1753) of the scientist Carolus Linnaeus' Systema Naturae will not be accepted. 

10. When the scientific name of a species is changed or corrected, the name of the first name-giver is in brackets must be placed in and the name of the new provider will be after the brackets. For example, Albizzia lebbeck (Linn.) Benth.

11. The genus and species part of an animal's scientific name may be the same. For example - Loa loa. This condition is called tautonym. 

12. The type specimen is the animal to be used as a specimen during naming and should be stored as a type specimen in the laboratory.

(D) Law of Priority Homonym and Synonym: 

This is a very controversial part of the naming of organisms. But it is the priority law of the International Code of Nomenclature (ICBN and ICZN) which maintains the stability of this code. When two organisms belonging to the same taxon have the same name, the problem of the validity of one of the names is resolved by the 'priority law'.

A single organism may have many names published in research papers or journals because different scientists have used different names at different times. But according to international rules, each species has only one valid scientific name. The valid name of a species is determined according to the law of priority. In this case, among multiple names of an organism, the first scientist to publish the name follows the rules of ICBN and ICZN. The name is considered valid. The remaining names are discarded.

Homonym: 

If two different organisms (plants or animals) belonging to the same kingdom are given the same name and the spelling and pronunciation of the names are the same, then they are called homonyms. The first given name (senior homonym) is considered valid and the later given name (junior homonym) is changed. For example, there are birds and insects called Noctua variegata. These two are homonyms and are not recognized in international norms.

Synonym:

If there are many names of the same species of organism (plant or animal), names other than valid or recognized names are called synonyms or synonyms. Synonyms published earlier are called senior synonyms and hilsa fish synonyms published later are called junior synonyms. For example - Tenualosa ilisha is the legal name of and synonyms are - Chupanodon ilisha / Clupea ilisha / Hilsa ilisha etc. Only senior homonyms and senior synonyms are considered valid names according to the law of precedence.

(E) Documentation: 

It is necessary to collect a specimen of an organism (plant or animal) after classifying it and storing it in a museum for the convenience of future scientists' identification, naming, and research.

Briefly, the main principles of classification are: 

• To classify, taxon should be included in successive categories or ranks. 
• Every Identifying feature of the taxon included in the category should be mentioned.
• Each taxon must have a scientific name. The nomenclature process has to be done properly following ICZN rules. 
• Classified samples shall be properly preserved. 
• Specific collection and preservation procedures should be followed for different groups of animals and there should be comparative descriptions with other related animals. 

The Necessity of Animal Classification:

The necessity of classification in both theoretical and applied biology is undeniable. The necessity of animal classification  is mentioned below:

Theoretical necessity:

• Knowledge of an animal belonging to a group of animals through classification leads to an understanding of other animals of that group. 
• Many members of the animal kingdom can be known and learned with little effort and in a short time.
• A variety of information is available on the interrelationships or genealogy of fauna. 
• Helps in determining the evolutionary process of animals. 
• Taxonomy is essential to identify new species. 
• The details of the animal ecosystem are known.

Applied necessity:

• By taxonomic identification of specific species for the purpose of control of species harmful to public health, agriculture, and forestry. 
• Animals of economic importance can be selected. 
• Helps in wildlife conservation.
• A classification of the biosphere is necessary to give a complete picture of the chronology. 
• Development of improved breeds of animals is facilitated through artificial breeding.