# Anatomy and Physiology of Animals/Classification

!original image by
R\'Eyes cc
by{width="400"}

## Objectives

After completing this section, you should know:

-   how to write the scientific name of animals correctly
-   know that animals belong to the Animal kingdom and that this is
    divided into phyla, classes, orders, families
-   know the definition of a species
-   know the phylum and class of the more common animals dealt with in
    this course

**Classification** is the process used by scientists to make sense of
the 1.5 million or so different kinds of living organisms on the planet.
It does this by describing, naming and placing them in different groups.
As veterinary nurses you are mainly concerned with the Animal Kingdom
but don't forget that animals rely on the Plant Kingdom for food to
survive. Also many diseases that animals are affected by are members of
the other Kingdoms---fungi, bacteria and single celled animals.

## Naming And Classifying Animals

There are more than 1.5 million different kinds of living organism on
Earth ranging from small and simple bacteria to large, complex mammals.
From the earliest time that humans have studied the natural world they
have named these living organisms and placed them in different groups on
the basis of their similarities and differences.

## Naming Animals

Of course we know what a cat, a dog and a whale are but, in some
situations using the common names for animals can be confusing. Problems
arise because people in different countries, and even sometimes in the
same country, have different common names for the same animals. For
example a cat can be a chat, a Katze, gato, katt, or a moggie, depending
on which language you use. To add to the confusion sometimes the same
name is used for different animals. For example, the name 'gopher' is
used for ground squirrels, rodents (pocket gophers), for moles and in
the south-eastern United States for a turtle. This is the reason why all
animals have been given an official **scientific** or **binomial name**.
Unfortunately these names are always in Latin. For example:

-   Common rat: *Rattus rattus*
-   Human: *Homo sapiens*
-   Domestic cat: *Felis domesticus*
-   Domestic dog: *Canis familiaris*

As you can see from the above there are certain rules about writing
scientific names:

-   They always have **2 parts** to them.
-   The first part is the **genus** name and is always written with a
    **capital** first letter.
-   The second name is the **species** name and is always written in
    **lower case**.
-   The name is always **underlined** or printed in **italics**.

The first time you refer to an organism you should write the whole name
in full. If you need to keep referring to the same organism you can then
abbreviate the genus name to just the initial. Thus "*Canis familiaris*"
becomes "*C. familiaris*" the second and subsequent times you refer to
it.

## Classification Of Living Organisms

To make some sense of the multitude of living organisms they have been
placed in different groups. The method that has been agreed by
biologists for doing this is called the **classification system**. The
system is based on the assumption that the process of evolution has,
over the millennia, brought about slow changes that have converted
simple one-celled organisms to complex multi-celled ones and generated
the earth's incredible diversity of life forms. The classification
system attempts to reflect the evolutionary relationships between
organisms.

Initially this classification was based only on the appearance of the
organism. However, the development of new techniques has advanced our
scientific knowledge. The light microscope and later the electron
microscope have enabled us to view the smallest structures, and now
techniques for comparing DNA have begun to clarify still further the
relationships between organisms. In the light of the advances in
knowledge the classification has undergone numerous revisions over time.

At present most biologists divide the living world into 5 kingdoms,
namely:

-   bacteria
-   protists
-   fungi
-   plants
-   animal

We are concerned here almost entirely with the **Animal Kingdom**.
However, we must not forget that bacteria, protists, and fungi cause
many of the serious diseases that affect animals, and all animals rely
either directly or indirectly on the plant world for their nourishment.

## The Animal Kingdom

So what are animals? If we were suddenly confronted with an animal we
had never seen in our lives before, how would we know it was not a plant
or even a fungus? We all intuitively know part of the answer to this.

Animals:

-   eat organic material (plants or other animals)
-   move to find food
-   take the food into their bodies and then digest it
-   and most reproduce by fertilizing eggs by sperm

If you were tempted to add that animals are furry, run around on four
legs and give birth to young that they feed on milk you were thinking
only of mammals and forgetting temporarily that frogs, snakes and
crocodiles, birds as well as fish, are also animals.

These are all members of the group called the **vertebrates** (or
animals with a backbone) and mammals make up only about 8% of this
group. The diagram on the next page shows the percentage of the
different kinds of vertebrates.

![](Proportions_of_different_kinds_of_vertebrate.JPG "Proportions_of_different_kinds_of_vertebrate.JPG")

However, the term animal includes much more than just the Vertebrates.
In fact this group makes up only a very small portion of all animals.
Take a look at the diagram below, which shows the size of the different
groups of animals in the Animal Kingdom as proportions of the total
number of different animal species. Notice the small size of the segment
representing vertebrates! All the other animals in the Animal Kingdom
are animals with no backbone, or **invertebrates**. This includes the
worms, sea anemones, starfish, snails, crabs, spiders and insects. As
more than 90% of the invertebrates are insects, no wonder people worry
that insects may take over the world one day!

![](Fraction_of_vertebrates_within_the_animal_kingdom.jpg "Fraction_of_vertebrates_within_the_animal_kingdom.jpg")

## The Classification Of Vertebrates

As we have seen above the Vertebrates are divided into 5 groups or
classes namely:

-   Fish
-   Amphibia (frogs and toads)
-   Reptiles (snakes and crocodiles)
-   Birds
-   Mammals

These classes are all based on similarities. For instance all mammals
have a similar skeleton, hair on their bodies, are warm bodied and
suckle their young.

The class Mammalia (the mammals) contains 3 **subclasses**:

-   **Monotremes** (Duck billed platypus and the echidna)
-   **Marsupials** (animals like the kangaroo with pouches)
-   **True mammals** (with a placenta)

Within the subclass containing the true mammals, there are groupings
called **orders** that contain mammals that are more closely similar or
related, than others. Examples of six mammalian orders are given below:

-   Rodents (Rodentia) (rats and mice)
-   Carnivores (Carnivora) (cats, dogs, bears and seals)
-   Even-toed grazers (Artiodactyla) (pigs, sheep, cattle, antelopes)
-   Odd-toed grazers (Perissodactyla) (horses, donkeys, zebras)
-   Marine mammals (Cetacea) (whales, sea cows)
-   Primates (monkeys, apes, humans)

Within each order there are various **families**. For example within the
carnivore mammals are the families:

-   Canidae (dog-like carnivores)
-   Felidae (cat-like carnivores)

Even at this point it is possible to find groupings that are more
closely related than others. These groups are called **genera**
(singular genus). For instance within the cat family Felidae is the
genus Felis containing the cats, as well as genera containing panthers,
lynxes, and sabre toothed tigers!

The final groups within the system are the **species**. The definition
of a species is a **group of animals that can mate successfully and
produce fertile offspring**. This means that all domestic cats belong to
the species *Felis domesticus*, because all breeds of cat whether
Siamese, Manx or ordinary House hold cat can cross breed. However,
domestic cats can not mate successfully with lions, tigers or jaguars,
so these are placed in separate species, e.g. *Felis leo, Felis tigris
and Felis onca*.

Even within the same species, there can be animals with quite wide
variations in appearance that still breed successfully. We call these
different **breeds, races** or **varieties**. For example there are many
different breeds of dogs from Dalmatian to Chihuahua and of cats, from
Siamese to Manx and domestic short-hairs, but all can cross breed. Often
these breeds have been produced by**selective breeding** but varieties
can arise in the wild when groups of animals are separated by a mountain
range or sea and have developed different characteristics over long
periods of time.

To summarise, the classification system consists of:

The **A**nimal **K**ingdom which is divided into

**P**hyla which are divided into

**C**lasses which are divided into

**O**rders which are divided into

**F**amilies which are divided into

**G**enera which are divided into

**S**pecies.

"**Kings Play Cricket On Flat Green Surfaces**" OR "**Kindly Professors
Cannot Often Fail Good Students**" are just two of the phrases students
use to remind themselves of the order of these categories - on the other
hand you might like to invent your own.

## Summary

-   The **scientific name** of an animal has two parts, the **genus**
    and the **species**, and must be written in **italics** or
    **underlined**.
-   Animals are divided into **vertebrates** and **invertebrates**.
-   The classification system has groupings called **phyla**,
    **classes**, **orders**, **families**, **genera** and **species**.
-   Furry, milk-producing animals are all in the class **Mammalia.**
-   Members within a **species** can mate and produce fertile offspring.
-   Sub-groups within a species include **breeds, races** and
    **varieties**.

## Worksheet

Work through the exercises in this Classification
Worksheet to help
you learn how to write scientific names and classify different animals.

## Test Yourself

1a) True or False. Is this name written correctly? trichosurus
Vulpecula.

1b) What do you need to change?

2\. Rearrange these groups from the biggest to the smallest:

:   a\) cars \| diesel cars \| motor vehicles \| my diesel Toyota \|
    transportation

```{=html}
<!-- -->
```

:   b\) Class \| Species \| Phylum \| Genus \| Order \| Kingdom \|
    Family

## Websites

### Classification

-   <http://www.mcwdn.org/Animals/AnimalClassQuiz.html> Animal
    classification quiz

In fact much more than that. There is an elementary cell biology and
classification quiz but the best thing about this website are the links
to tables of characteristics of the different animal groups, for animals
both with and without backbones.

-   <http://animaldiversity.ummz.umich.edu/site/index.html> Animal
    diversity web

Careful! You could waste all day exploring this wonderful website. Chose
an animal or group of animals you want to know about and you will see
not only the classification but photos and details of distribution,
behaviour and conservation status etc.

-   <http://www.indianchild.com/animal_kingdom.htm> Indian child

Nice clear explanation of the different categories used in the
classification of animals.

## Glossary

-   Link to
    Glossary

