Editing Priapulida (section)

=== Reproduction and development ===
For the species ''Priapulus caudatus'', the 80&nbsp;μm egg undergoes a total and radial cleavage following a symmetrical and subequal pattern.<ref name=Wennberg2008>{{Cite journal | last1 = Wennberg | first1 = S. A. | last2 = Janssen | first2 = R. | last3 = Budd | first3 = G. E. | doi = 10.1111/j.1525-142X.2008.00241.x | title = Early embryonic development of the priapulid worm ''Priapulus caudatus'' | journal = Evolution & Development | volume = 10 | issue = 3 | pages = 326–338 | date = May–June 2008 | pmid = 18460094| s2cid = 11175247 | url = http://uu.diva-portal.org/smash/get/diva2:172287/FULLTEXT01 }}</ref> Development is remarkably slow, with the first cleavage taking place 15 hours after fertilization, gastrulation after several days and hatching of the first 'lorica' larvae after 15 to 20 days.<ref name="Janssen-2009">{{Cite journal | last1 = Janssen | first1 = R. | last2 = Wennberg | first2 = S. A. | last3 = Budd | first3 = G. E. | title = The hatching larva of the priapulid worm ''Halicryptus spinulosus'' | doi = 10.1186/1742-9994-6-8 | journal = Frontiers in Zoology | volume = 6 | page = 8 | date = 26 May 2009 | pmid = 19470151| pmc = 2693540 | doi-access = free }}</ref> The species ''Meiopriapulus fijiensis'' have direct development.<ref>{{cite journal |title=Evidence for Direct Development in Meiopriapulus fijiensis (Priapulida) |journal=Transactions of the American Microscopical Society |volume=110 |issue=1 |pages=37–46 |date=January 1991 | jstor = 3226738 |last1=Higgins |first1=Robert P. |last2=Storch |first2=Volker |doi=10.2307/3226738 }}</ref> In current systematics, they are described as protostomes, despite having a deuterostomic development.<ref>{{Cite journal | doi = 10.1016/j.cub.2012.09.037|title = Deuterostomic development in the protostome ''Priapulus caudatus'' | journal = Current Biology| volume = 22| issue = 22| pages = 2161–2166 | year = 2012| last1 = Martín-Durán | first1 = J. M. | last2 = Janssen | first2 = R. | last3 = Wennberg | first3 = S. | last4 = Budd | first4 = G. E. | last5 = Hejnol | first5 = A. | pmid=23103190| doi-access = free |bibcode = 2012CBio...22.2161M }}</ref> Because the group is so ancient, it is assumed the deuterostome condition which appears to be ancestral for [[Nephrozoa|bilaterians]] have been maintained.<ref>{{cite web| url = https://www.sciencedaily.com/releases/2012/10/121026084350.htm| title = Penis worms show the evolution of the digestive system}}</ref>