 Some studies have shown that sponges do not form a monophyletic group, in other words do not include "all and only" the descendants of a common ancestor.Recent phylogenetic analyses suggest that comb jellies rather than sponges are the sister group to the rest of animals.The few species of demosponge that have entirely soft fibrous skeletons with no hard elements have been used by humans over thousands of years for several purposes, including as padding and as cleaning tools.