In accordance with their life styles, parasites evolved special adaptations.

These are the loss of unnecessary sense organs, presence of adhesive organs or suckers to cling on to the host (e.g. suckers in tape worm), loss of digestive system (e.g. tapeworm) high reproductive capacity (e.g. roundworm).

The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of its primary host.