The key characteristic of all animals is movement. They achieve this in many different ways. Microscopic organisms such as bacteria have a flagellum that they can wiggle to propel themselves. Spiders use passive movement whenever they glide downwards. Mammals self-propel to crawl, walk and run. Aquatic organisms have fins to move underwater. Birds use wings to fly through the air.

There are more specific, intermediate types of movement such as gliding, soaring, jumping and climbing. Some insects can jump very high in the air. Parasites are transported by their hosts, an indirect method of transportation that can nonetheless be very powerful.

In order to have locomotion, animals evolved structures that could support the added pressure of navigating terrestrial environments, the water, the air, etc. These come in the form of external or internal skeletons which provide…