There are about 60,000 species of arachnids.
Arachnids have eight legs, not six like insects. They also have an extra pair of either pincers or fangs.
They do not have wings or antennae but they do have a hard exoskeleton.
Arachnids have two parts to their body - the cephalothorax and the abdomen. The cephalothorax is like the head and thorax section of an insect but it is fused together. It contains the legs, mouth parts and sense organs. The abdomen contains the main organs, just like insects.
Arachnids are usually predators. This means they eat other creatures so must hunt for their food. Spiders spin webs to catch prey and scorpions have stinging tails and pincers to catch and kill their food.
Arachnids tend to kill their prey with poisonous fangs then inject digestive juices to dissolve the flesh before sucking it up!