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Classification of animals and plants

 The animals are numerous and different in a living environment: we show great diversity. However, if we compare them, we can find similarities that allow us to classify them as groups.

- What common criteria make it possible to group these animals?

- How to use a key for determining living beings?

To classify animals, we first identify one or more criteria then they are grouped according to the presence or absence of this (s) criterion(es) they have in common.

For example:

If the "vertebral column" criterion is chosen, the animals can be classified into two groups:

The vertebrates :

If the "skin coating" criterion is chosen, the vertebrates

can be divided into 5 classes:

- Fish: skin covered with scales that can be detached one by one.

- Amphibians: moist bare skin.

- Reptiles: skin covered with fused scales.

- Birds: skin covered with feathers.

- Mammals: skin covered with hair.

image 1: The vertebrates


Invertebrates can be classified according to several criteria:

- Presence or absence of legs

- Body consistency

- Body joint

- Body symmetry

- Presence or absence of shell...

For example, if we take the criterion "presence or absence of legs", we distinguish:

- Presence of legs

➢ Insects (3 pairs of legs)

➢ Arachnids (4 pairs of legs)

➢ Crustaceans (5 pairs of legs or more).

➢ Myriapods (several pairs of legs)

- Absence of legs:

➢ worms.

➢ mollusks

➢ echinoderms

➢ cnidarians

We must not forget the unicellular animal beings called the

zooplankton (consisting of a single cell).