Classification

Classification 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
Scientific 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.

A 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 key below.