The rich morphological diversity among echinoderms is a major source of our fascination with this group of marine creatures; however, this is also a source of confusion. Through the history of echinoderm study, different terminologies have developed such that understanding relationships between major groups can be problematic. For example, the term radial plate may be used for non-homologous characters between two different groups, and the homologous feature to a radial plate in one group may be given a different name in another.
Sumrall established a set of characters in the region of the mouth that can easily be compared among pelmatozoans. This method, Universal Elemental Homologies (UEH), can also be applied to crinoids. This methodology will be used to test various hypotheses for crinoid origination, such as the following hypotheses: What were the immediate ancestors of the Crinoidea:
(III) or one of the pelmatozoans?
If hypothesis III, based on UEH which pelmatozoan group is the sister group to crinoids?