Complex sentence: The descriptor, "white tail", is applied to a variety of species of spiders for which a distal white mark on their abdomen is a distinctive feature; other markings disappear with moultings but the white tail remains to adulthood.
Split into simpler sentences: The descriptor, "white tail", is applied to a variety of species of spiders for which a distal white mark on their abdomen is a distinctive feature. While other markings disappear with moultings the white tail remains to adulthood.