Biology 2nd Paper (Zoology) · Classes 11-12 · Chapter 1

Principles of Classification and Nomenclature.

A human's full address in classification takes seven lines, from Kingdom Animalia down to Species Homo sapiens. Even the way that name is written has rules: the genus with a capital, the species with a small letter, and italics in print. This note puts the ranks, their definitions and the naming rules in one place.

1. The five principles

Classification rests on five principles: determining taxonomic characters, identification, categorisation or ranking, nomenclature and preservation. The rest of this note unpacks these five.

A feature that separates the members of one taxon from another is that taxon's taxonomic character. In modern research these include morphological, chemical, physiological, genetic, reproductive and ecological characters.

When a specimen is identified it may be known or unknown. Unknown does not mean a new taxon. It is compared, by a set method, with the published descriptions of related animals, and only then categorised.

2. Taxa and the seven ranks

Each group of animals placed in a step, or rank, of classification is a taxon (plural taxa). A taxon is a taxonomic unit. Animalia, Chordata, Mammalia, Primates, Hominidae, Homo and Homo sapiens are each a taxon.

The mandatory ranks are seven: Kingdom, Phylum, Class, Order, Family, Genus and Species. As more and more animals were discovered, levels such as Super, Sub and Infra were added to these seven. They are not mandatory ranks.

From largest to smallest the ranks run kingdom, phylum, class, order, family, genus, species. The kingdom is the largest and the species the smallest. Arrange them yourself.

The species is the basic unit of classification. By Ernst Mayr (1969), a natural group whose members interbreed to produce fertile offspring, yet are reproductively isolated from other groups, is a species.

From there, each rank is built from the one below. Several similar species make a genus. One or more similar genera make a family. One or more similar families make an order. One or more related orders make a class. And several similar classes make a phylum.

At the top is the kingdom. It is the universal level of animal classification and includes all animals of the earth. Tap the grid to match each rank with what it holds.

The human's position (Figure 1.10): Kingdom Animalia, Phylum Chordata, Class Mammalia, Order Primates, Family Hominidae, Genus Homo, Species Homo sapiens. This sequence of levels used in animal classification is called the Linnaean hierarchy. Open the nodes one by one. Homo is the genus, and the order is Primates.

3. Nomenclature and its rules

Nomenclature is the method of identifying an animal or a group of animals by a fixed name. When a new animal is proven, it must be named by the rules of ICZN.

The Swedish scientist Carolus Linnaeus first introduced a system of naming, called binomial nomenclature. The scientific name has two parts: the genus name first, starting with a capital letter, and the species name second, starting with a small letter. Both are Latin or Latinised words.

ICZN stands for the International Commission on Zoological Nomenclature, the international body that makes the rules for naming animals. The rules are written in the International Code on Zoological Nomenclature.

First rule: the scientific name must be Latin or Latinised and always printed in italics, that is, in type that slants to the right, e.g. Panthera tigris (tiger). Second rule: the genus name is a noun with a capital first letter. The species name is an adjective with a small first letter.

Now write a name yourself. Press a switch to break a rule and see which line turns red; add a subspecies or a describer and watch the name change.

Third rule: the name of the scientist who first describes an animal scientifically, or part of it, is added at the end of the binomial, e.g. Fejervarya asmati Howlader, 2011.

Members of one species with notable structural differences are subspecies. Naming with genus, species and subspecies, three words in all, is trinomial nomenclature. Schlegel (1844) introduced it, e.g. Passer domesticus niloticus. Now check six names.

4. Preserving specimens

A classified specimen must be preserved with full details: the collector's name, place, time and date. That makes it easier to identify other specimens later.

An animal body can be preserved dry or in liquid. Formalin and alcohol are good liquid media for preservation.

5. Check yourself

Three questions in the exam's style. Start with the first.

In the second, recall the order and the definitions of the ranks.

In the last, keep the naming rules in mind.

The whole note on seven cards.

Source: Biology 2nd Paper (Zoology), Classes 11-12 (NCTB), Chapter 1 “Animal Diversity and Classification”, the “Principles of Classification and Nomenclature” part.