Editing Hyolitha (section)

== Phylogenetic position  ==
[[File:Haplophrentis Burgess Shale.jpg|thumb|''Haplophrentis carinatus'' from the Stephen Formation, [[Burgess Shale]] (Middle [[Cambrian]]), Burgess Pass, British Columbia, Canada.]]
Because hyoliths are extinct and do not obviously resemble any [[Extant taxon|extant]] group, it has long been unclear which living group they are most closely related to.  They have been supposed to be molluscs; or to belong to their own phylum in an unspecified part of the tree of life.<ref name=Sumrall2009>{{cite journal |pages=147–152 |doi=10.1666/08-094R.1 |jstor=29739075 |title=Permian Hyolithida from Australia: The Last of the Hyoliths? |journal=Journal of Paleontology |volume=83 |issue=1 |year=2009 |last1=Malinky |first1=John M.}}</ref>  Their grade of organization was historically considered to be of the 'mollusc-annelid-sipunculid' level,<ref name="Runnegar1980">{{cite journal |last1=Runnegar |first1=B. |doi=10.1111/j.1502-3931.1980.tb01025.x |title=Hyolitha: Status of the phylum |journal=Lethaia |volume=13 |pages=21–25 |date=January 1980 }}</ref> consistent with a Lophotrochozoan affinity, and comparison was primarily drawn with the molluscs or [[sipunculid]]s.<ref name="Runnegar1980" /><ref name="Kouchinsky2000">{{cite journal |last1=Kouchinsky |first1=A. V. |title=Skeletal microstructures of hyoliths from the Early Cambrian of Siberia |doi=10.1080/03115510008619525 |journal=Alcheringa: An Australasian Journal of Palaeontology |volume=24 |issue=2 |pages=65–81 |year=2000 |s2cid=140660142 }}</ref> Older studies (predating the Lophotrochozoan concept) consider hyoliths to represent a stem lineage of the clade containing (Mollusca + Annelida + Arthropoda).<ref name="Runnegar1975" />

A secure classification at last became possible in 2017, on the basis of [[Burgess Shale]] specimens that preserve lophophores. This diagnostic characteristic demonstrates an affinity with the [[Lophophorata]], a group that contains [[Brachiopoda]], [[Bryozoa]] (perhaps), and [[Phoronida]].<ref name="ReferenceA"/>

A study in 2019 estimated that hyoliths are more likely to be basal members of the [[lophotrochozoa]]ns rather than lophophorates.<ref name=":0" /> Meanwhile, a study in 2020 instead concluded that hyoliths belong to [[Mollusca]],<ref name=":1">{{Cite journal |last1=Li |first1=Luoyang |last2=Skovsted |first2=Christian B. |last3=Yun |first3=Hao |last4=Betts |first4=Marissa J. |last5=Zhang |first5=Xingliang |date=2020-08-26 |title=New insight into the soft anatomy and shell microstructures of early Cambrian orthothecids (Hyolitha) |journal=Proceedings of the Royal Society B: Biological Sciences |volume=287 |issue=1933 |pages=20201467 |doi=10.1098/rspb.2020.1467 |pmc=7482263 |pmid=32811320}}</ref> as did a different study in 2022.<ref name="LiSkovstedTopper2022" />