Editing Sipuncula (section)

==Fossil record==
[[File:Lecthaylus gregarius 5.jpg|thumb|''Lecthaylus gregarius'', a sipunculan from the Silurian of Illinois.]]

Because of their soft-bodied structure, fossils of sipunculans are extremely rare, and are only known from a few genera.  ''[[Archaeogolfingia]]'' and ''[[Cambrosipunculus]]'' appear in the [[Cambrian]] [[Maotianshan Shales|Chengjiang biota]] in China. These fossils appear to belong to the [[crown group]],<ref name="Huang2004">{{Cite journal | last1 = Huang | first1 = D. -Y. | last2 = Chen | first2 = J. -Y. | last3 = Vannier | first3 = J. | last4 = Saiz Salinas | first4 = J. I. | title = Early Cambrian sipunculan worms from southwest China | doi = 10.1098/rspb.2004.2774 | journal = Proceedings of the Royal Society B: Biological Sciences | volume = 271 | issue = 1549 | pages = 1671–6 | date = 22 August 2004 | pmid =  15306286| pmc = 1691784}}</ref><ref name="Eibye-Jacobsen2012">{{Cite journal | last1 = Eibye-Jacobsen | first1 = D. | last2 = Vinther | first2 = J. | doi = 10.1111/j.1439-0469.2011.00651.x | title = Reconstructing the ancestral annelid | journal = Journal of Zoological Systematics and Evolutionary Research | volume = 50 | pages = 85–87 | date = February 2012 }}</ref> and demonstrate that sipunculans have changed little (morphologically) since the early Cambrian, about 520 million years ago.<ref name="Huang2004" />

An unnamed sipunculid worm from the Cambrian period has been discovered in the [[Burgess Shale]] in [[Alberta, Canada]],<ref name="Caron2010">{{Cite journal| last1 = Caron | first1 = J. -B.| last2 = Gaines | first2 = R. R.| last3 = Mangano | first3 = M. G.| last4 = Streng | first4 = M.| last5 = Daley | first5 = A. C.| title = A new Burgess Shale-type assemblage from the "thin" Stephen Formation of the southern Canadian Rockies| journal = Geology| volume = 38| issue = 9| pages = 811–814| year = 2010| doi = 10.1130/G31080.1| bibcode = 2010Geo....38..811C| url = https://scholarship.claremont.edu/cgi/viewcontent.cgi?article=1104&context=pomona_fac_pub}}</ref> and ''[[Lecthaylus]]'' has been identified from the [[Granton Shrimp Bed]], near Edinburgh, Scotland, dating to the [[Silurian]] period.<ref name="Muir2007">{{Cite journal | last1 = Muir | first1 = L. A. | last2 = Botting | first2 = J. P. | doi = 10.1144/sjg43010051 | title = A Lower Carboniferous sipunculan from the Granton Shrimp Bed, Edinburgh | journal = Scottish Journal of Geology | volume = 43 | pages = 51–56 | year = 2007 | issue = 1 | bibcode = 2007ScJG...43...51M | s2cid = 131119101 }}</ref> [[Trace fossil]]s of burrows that may have been formed by sipunculans have been found from the [[Paleozoic]].<ref name="Huang2004" />

Some scientists once hypothesized a close relationship between sipunculans and the extinct [[hyolith]]s, [[Operculum (gastropod)|operculate]] shells from the [[Palaeozoic]] with which they share a helical gut; but this hypothesis has since been discounted.<ref>{{cite journal |author1=Moysiuk,Joseph |author2=Smith, Martin R. |author3=Caron, Jean-Bernard |year=2017 |title=Hyoliths are Palaeozoic lophophorates |journal=Nature |volume=541 |issue=7637 |pages=394–397 |doi=10.1038/nature20804 |pmid=28077871 |bibcode=2017Natur.541..394M |s2cid=4409157 |url=http://dro.dur.ac.uk/20195/1/20195.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://dro.dur.ac.uk/20195/1/20195.pdf |archive-date=2022-10-09 |url-status=live }}</ref>