Nomenclature methods and Basic principles of nomenclature and Identification keys

Nomenclature methods

Nomenclature forms the basis by which scientists can name and cross refer to organisms. It is an integral part of taxonomy. In fact, modern tax-onomy started in 1753 with the publication of first part of Systema by Linnaeus. According to Linnaeus a Species is specified by the combination of both its specific and generic names. Since it requires two names, it is referred to as the binomial system. This system is now firmly established in Biology.

In modern times International Commissions are responsible for nam-ing each major group of organisms. There are several such commissions. These commissions authorize the usage of scientific names in biology. Naming of animals is monitored by International Code of Zoological Nomenclature (ICZN) (International Commission of Zoological Nomenclature, 1985).

The rules are set out in the 'codes'. The codes are modified by occasional science congresses.

Basic principles of nomenclature

1.    Providing stability in the naming and classification of organisms is emphasized. Any taxon must have only one correct name.

2.   If two or more names are already in use the correct name will be the one that was published earlier. This system is referred to as the law of priority.

3.  If two or more workers at one particular time describe the same organism using different names, it results in synonyms. However only one name will be held as a valid name. The validity is provided to the senior synonym.(law of priority)

4.    When names referring to two separate taxa of the same nomenclatural level are spelt the same, the two names are called homonyms. This situation arises when two separate authors used the same name to refer to two differ-ent taxa. This condition is called homonymy. In this situation the junior name is invalid and a newreplacement has to be proposed.

5.  A material on which an original description is based, gets a special status. It will form the basis for any future identity of a taxon. This idea is called the type concept. Thus the concept of a genus and species are fixed by their type genus or type species.

6.   Names that were used prior to those included by Linnaeus in the 'Systema Naturae', tenth edition, 1758 are not recognised.

7.    Scientific names must be either Latin or latinized. The name should be mentioned in italics.

8.  The genus name should be a single word beginning with a capital letter.

9.   The species name sholud be a single or compound word beginning with a smalll letter.

Identification keys

Identification of animals is an integral part of taxonomy. Identification could be made thorugh literature, keys, pictures and comparison with type specimens. Of these, the most commonly used method is, using of keys.

A key is essentially a printed information or a computer software pack-age. The construction of the key is an important job of a systematist.

A good key is strictly dichotomous and not having more than two al-ternatives at any point. The language of a key is telegraphic.

The key may be either bracketed or indented. In a bracketed key alternative contrastive characters are used for identification. The number on the right side indicates the next alternative character for consideration.

In an indented key a series of choices are provided for identifying a taxon. The user should choose from among the choices.

The following examples provide the keys for identification four species of frogs in Tamil Nadu, namely Rana hexadactyla, R. tigrina,

R. cyanophlictis and R. limnochoris.

The Bracketed key (Genus : Rana)

(1) Large size, snout - vent 100 - 200mm... 3

(1) Small size,snout to vent less than 100 mm... 2

(2) Pointed snout.................................. R. limnochoris

(2) Obtusely pointed snout.............. R. hexadactyla

(3) 4th  toe longer than others.......... R. tigrina

(3) 4th  toe not longer........................... R. cyanophlictis.

The Indented key (Genus : Rana)

Large sized body

skin smooth............................... R.hexadactyla

skin with folds.......................... R. tigrina

Small size

blunt snout................................. R. cyanophlictis

pointed or round snout............. R. limnochoris