Acanthocephala
The Acanthocephala were thought to be a separate phylum. Recent genome analysis has shown that they are closely related to rotifers. Since all parasites are derived from free-living forms, the Acanthocephalans are modified rotifers. This is an example of molecular phylogenetics. In due course, spiny-headed worms will probably be placed in a taxonomic rank below phylum, such as sub-phylum or class.