CLASSIFICATION
It is natural for humans to recognize the features of living organisms and to use these features to put organisms into
groups. At a basic level, simple observation shows that there are often many organisms of the same type. If we agree
on a name for a group of organisms, we can then talk or write about them. Naming organisms is called
nomenclature. The system that biologist use to name species is called binomial nomenclature because it consists of
two words: one of the genus and the second of the species. Example: Linnaea borealis. The genus is a group of
species that share certain characteristics. The second name is the species-specific name.
This system of naming organisms was proposed by the Swedish naturalist Carolus Linnaeus in his book Systema
Naturae (The natural World, 1735).
Rules for naming organisms:
 The genus name begins with an upper-case (capital) letter and the species name with a lower-case (small)
letter.
 In typed or printed text, a binomial is shown in italics.
 After a binomial has been used once in a piece of text, it can be abbreviated to the initial letter of the genus
name with the full species name, for example: L. borealis.
 The earliest published name for a species, from 1753 onwards, is the correct one.
Hierarchy of taxa
The word taxon is Greek and means things that are arranged into a group. The plural is taxa. In biology, species are
arranged or classified into taxa. There are seven levels of classification. Going up in hierarchy, the taxa include larger
and larger numbers of species, which share fewer and fewer features:
Taxon
Kingdom
Phylum
Class
Order
Family
Genus
Species
Grey wolf
Animalia
Chordata
Mammalia
Carnivora
Canidae
Canis
lupus
Five Kingdoms:
Plantae (plants: cantus, moss)
Date palm
Plantae
Angiospermophyta
Monocotyledoneae
Palmales
Arecaceae
Phoenix
dactylifera
Truffle
Fungi
Ascomycota
Pezizomycetes
Pezizales
Tuberaceae
Tuber
melanosporum
Characteristics
Animalia (animals: spider, humans)
Fungi (fungi and moulds: Penicillium,
Aspergillus)
Protoctista (the protozoa and algae:
Paramecium ad seaweed)
Prokaryotae (the bacteria:
Streptococcus, Salmonella)
Human classification:
The classification of humans has caused more controversy than any other species. One reason for this is that natural
classification indicates the probable evolutionary origins of a species. Using the standard taxonomic procedures,
humans are assigned to the order Primates and the family Hominidae. There has been much debate about which, if
any, of the great apes to include in this family. Originally, all the greater apes were placed in another family, the
Pongidae, but research has shown that chimpanzees and gorillas are closer to humans than to orangutans in the
Pongidae. Most evidence suggests that chimpanzees are closer than gorillas to humans, so if humans and
chimpanzees are placed in different genera, gorillas should also be in a separate genus. A summary of this scheme
for human classification is shown in the figure.
FAMILY
GENUS
AND
SPECIES
Hominidae
Gorilla
Gorilla
(gorilla)
Homo
sapiens
(human)
Pongidae
Pan
Pan
troglodytes
paniscus
(chimpanzee) (bonobo)
Pongo
pygmaeus
(orangutan)
Plant classification: Most plants are in one of these four phyla.
Plant phyla
Characteristics
Angyospermophyta
Coniferophyta
Filicinophyta
Bryophyta
Animal Classification: animals are classified into over 30 phyla based on their characteristics. Six phyla are featured
here.
Plant phyla
Characteristics
Porifera
Cnidaria
Platyhelminthes
Mollusca
Annelida
Arthropoda
Dichotomous keys
The hierarchy of taxa can be used to help identify an organism. It is obvious what kingdom a species belongs to, and
often the phylum and class are easily recognized as well. Going down through the lower taxa, through the order,
family, genus and species, a point is often reached where the ecologist needs help to assign a species to the correct
group. Keys are used for this.
A dichotomy is a division into two; a dichotomous key consists of a numbered series of pairs of descriptions. One of
these should clearly match the species and the other should clearly be wrong. The features that the designer of the
key chooses to use in the descriptions should therefore be reliable and easily visible. Each of the pair of descriptions
leads either to another of the numbered pairs of descriptions in the key, or to an identification.
Work on the following dichotomous key of Norno identification:
Dichotomous Key on Norns
1. Has pointed ears ................................................. go to 3
....Has rounded ears ................................................go to 2
2. Has no tail ........................................................... Kentuckyus
....Has tail ................................................................ Dakotus
3. Ears point upward ................................................. go to 5
....Ears point downward .............................................go to 4
Norns belong to the genus
Norno and can be divided into
eight species that are generally
located in specific regions of the
world. Use the dichotomos key
to identify the norns below. Write
their complete scientific name
(genus + species) in the blank.
4. Engages in waving behavior ................................ Dallus
....Has hairy tufts on ears ..........................................Californius
5. Engages in waving behavior ............................... WalaWala
....Does not engage in waving behavior....................go to 6
6. Has hair on head ............................................. Beverlus
....Has no hair on head (may have ear tufts) .......go to 7
7. Has a tail ........................................................ Yorkio
....Has no tail, aggressive ................................... Rajus
A______________________ B_____________________
C____________________
D_______________________ E______________________ F_____________________
G_____________________
H_______________________
Activities:
1. Draw one specimen for each of the plant phyla: (4)
2. Draw on specimen for each of the animal phyla: (6)
3. Use the leaves provided to create your own dichotomous
key: (10)
4. Animal phyla identification:
a. Study the organisms shown in the figure and assign each
one to its phylum. (7)
b. list the organisms that are:
i. bilaterally symmetric
ii. radially symmetric
iii. non symmetrical in their structure (3)
c. List the organisms that have:
i. jointed appendages
ii. stinging tentacles
iii. bristles (3)
d. List the organisms that filter feed by pumping water
through tubes inside their bodies (2)
Sources:
Allot, A., & Mindorff, D. (2010). Biology Course Companion. New Yorl: Oxford University Press.
Damon, A., McGonegal, R., Tosto , P., & Ward, W. (2007). Biology Higher Level. New Jersey: Pearson.