Halkieriids and Siphogonotuchids
Further information: HalkieriidMost of the debate has been about halkieriids' relationship to molluscs, annelids and brachiopods. However a paper published in 2008 argued that halkieriids were closely related to chancelloriids, which have been generally regarded as sponges.
Read more about this topic: Debate About Cambrian Lophotrochozoans