Cave dwelling, or troglophilic, animals spend their whole lives in cave systems. Living in perpetual darkness, many cave species have lost the sight that their evolutionary ancestors had and become blind. Vestigial eyes can often be seen. They're also usually pale in colour as they don't need to produce skin pigment as camouflage or protection from the sun.
Take a trip through the natural world with our themed collections of video clips from the natural history archive.