is an essential part of science. Scientists use observation-based
criteria when classifying the animals which make up the large
group known as arthropods and the smaller class called arachnids.
We will compare two arachnids, a spider
and a scorpion, in order to recognise the similarities
and differences between them.
classification systems are hierarchical. This is a useful way
of ordering things because it makes communication easier and
simplifies the description of things. Scientific classification
systems aim to reflect current knowledge about things. However,
when new information is discovered and interpreted, the classification
systems may need to be modified.
classification system for arthropods
which is currently in common use is shown in the diagram below.
The broadest category is arthropods, and is composed of a number
of classes which include, insects, arachnids, crustaceans and
myriapods. Each class can be further broken down, so that the
animals become more and more similar. For example, arachnids
can be broken down into the sub-groups of scorpions, spiders,
ticks and mites. This is represented in the classification