Priapulida

{{Short description|Phylum of unsegmented marine worms}} {{Automatic taxobox | fossil_range = {{geological range|Lower Cambrian|Recent|ref=<ref name=Budd2000 />|PS=(Stem-group from Cambrian)}} | image = Priapulus caudatus.jpg | image_caption = ''Priapulus caudatus'' | display_parents = 7 | taxon = Priapulida | authority = Théel, 1906<ref>{{cite journal|last1=Théel|first1=Hjalmar|title=Northern and Arctic Invertebrates in the Collection of the Swedish State Museum (Riksmuseum). II. Priapulids, Echiurids etc.|journal=Kungl. Svenska Vetenskapsakademiens Handlingar|volume=40|issue=4|pages=8–13|url=https://www.biodiversitylibrary.org/page/37205953|date=1905–1906}}</ref> | subdivision_ranks = Orders | subdivision = *Priapulimorpha *Halicryptomorpha {{small|Stem group order}} *Ottoimorpha {{small|also see text}} }}

'''Priapulida''' ('''priapulid worms''', from Gr. πριάπος, ''priāpos'' 'Priapus' + Lat. ''-ul-'', diminutive), sometimes referred to as '''penis worms''', is a phylum of unsegmented marine worms. The name of the phylum relates to the Greek god of fertility, because their general shape and their extensible spiny introvert (eversible) proboscis may resemble the shape of a human penis.

They live in the mud, except for a few tropical meiobenthic species which live in medium- to coarse-grained sands, and are found in comparatively shallow waters to deep waters, with the larger forms like Priapulidae being restricted to colder environments, and smaller forms like Tubiluchus requiring warmer temperatures.<ref name="EB1911" /><ref>{{cite journal|last1=Turk |first1=Katherine A. |last2=Wehrmann |first2=Achim |last3=Laflamme |first3=Marc |last4=Darroch |first4=Simon A. F. |title=Priapulid neoichnology, ecosystem engineering, and the Ediacaran–Cambrian transition |journal=Palaeontology |date=2024 |volume=67 |issue=4 |article-number=e12721 |doi=10.1111/pala.12721 |bibcode=2024Palgy..6712721T |url=https://onlinelibrary.wiley.com/doi/10.1111/pala.12721 |doi-access=free}}</ref><ref>[https://www.sealifebase.se/summary/Priapulus-caudatus.html Priapulus caudatus, Cactus worm]</ref><ref>{{cite journal | last1=Schmidt-Rhaesa | first1=Andreas | last2=Freese | first2=Maria | title=Microscopic priapulid larvae from Antarctica | journal=Zoologischer Anzeiger | date=2019 | volume=282 | page=3 | doi=10.1016/j.jcz.2019.06.001 | bibcode=2019ZooAn.282....3S | url=https://www.sciencedirect.com/science/article/abs/pii/S0044523119300713 | url-access=subscription }}</ref><ref>[https://repository.naturalis.nl/pub/317612/ZV1970112001.pdf Systematics, zoogeography, and ecology of the Priapulida]</ref> Most meiobenthic forms live as shallow as 0.5 m, and Priapulus abyssorum has been found on depths of 3000–8000 m.<ref>[https://uu.diva-portal.org/smash/get/diva2:172290/FULLTEXT01.pdf Aspects of priapulid development]</ref><ref>[https://www.sciencedirect.com/science/article/pii/S0044523124000779 New morphological structures of Priapulus caudatus, Lamarck 1816 (Priapulida) and analysis of homologous characters across macroscopic priapulids]</ref> Some species show a remarkable tolerance for hydrogen sulfide, anoxia and low salinity.<ref>{{Cite journal | doi = 10.1007/BF00017494| title = Histological studies on Halicryptus spinulosus (Priapulida) with regard to environmental hydrogen sulfide resistance| journal = Hydrobiologia| volume = 222| pages = 1–12| date = September 1991| last1 = Oeschger | first1 = R. | last2 = Janssen | first2 = H. H. | issue = 1| bibcode = 1991HyBio.222....1O| s2cid = 31342308}}</ref><ref>{{Cite journal |last1=Kolbasova |first1=Glafira |last2=Schmidt-Rhaesa |first2=Andreas |last3=Syomin |first3=Vitaly |last4=Bredikhin |first4=Danila |last5=Morozov |first5=Taras |last6=Neretina |first6=Tatiana |date=January 2023 |title=Cryptic species complex or an incomplete speciation? Phylogeographic analysis reveals an intricate Pleistocene history of Priapulus caudatus Lamarck, 1816 |journal=Zoologischer Anzeiger |language=en |volume=302 |pages=113–130 |doi=10.1016/j.jcz.2022.11.013|bibcode=2023ZooAn.302..113K |doi-access=free }}</ref> ''Halicryptus spinulosus'' appears to prefer brackish shallow waters.<ref>[https://www.zin.ru/journals/zsr/content/1996/zr_1996_5_1_Adrianov.pdf The phylogeny, classification and zoogeography of the class Priapulida. II. Revision of the family Priapulidae and zoogeography of priapulids]</ref> They can be quite abundant in some areas. In an Alaskan bay as many as 85 adult individuals of ''Priapulus caudatus'' per square meter has been recorded, while the density of its larvae can be as high as 58,000 per square meter (5,390 per square foot).<ref>{{cite book| url = https://books.google.com/books?id=9IWaqAOGyt4C&dq=85+adults+per+square+meter&pg=PA286| title = Kingdoms and Domains: An Illustrated Guide to the Phyla of Life on Earth| isbn = 978-0-08-092014-6| last1 = Margulis| first1 = Lynn| author1-link = Lynn Margulis | last2 = Chapman| first2 = Michael J.| date = 19 March 2009| publisher = Academic Press}}</ref> They feed on slow-moving invertebrates, such as polychaete worms. Twenty-two extant species of priapulid worms are known, half of them being of meiobenthic size.<ref>{{cite book |last1=Giere |first1=Olav |url=https://books.google.com/books?id=an9ncYOxkUoC&dq=priapulida+%2220+species%22&pg=PA158 |title=Meiobenthology: The Microscopic Motile Fauna of Aquatic Sediments |date=November 2008 |publisher=Springer |isbn=978-3-540-68661-3}}</ref>

Together with Echiura and Sipuncula, they were once placed in the taxon Gephyrea, but consistent morphological and molecular evidence supports their belonging to Ecdysozoa, which also includes arthropods and nematodes. Fossil findings show that the mouth design of the stem-arthropod ''Pambdelurion'' is identical with that of priapulids, indicating that their mouth is an original trait inherited from the last common ancestor of both priapulids and arthropods, even if modern arthropods no longer possess it.<ref>{{cite web| url = https://phys.org/news/2016-09-ancestor-arthropods-mouth-penis-worm.html| title = Ancestor of arthropods had the mouth of a penis worm}}</ref>

The precise phylogenetic placement of Priapulida within Ecdysozoa remains unresolved, in part due to a lack of genomic and transcriptomic resources.<ref name=":0">{{Cite journal |last=Giribet |first=Gonzalo |last2=Edgecombe |first2=Gregory D. |date=Sep 2017 |title=Current Understanding of Ecdysozoa and its Internal Phylogenetic Relationships |url=http://academic.oup.com/icb/article/57/3/455/4093795/Current-Understanding-of-Ecdysozoa-and-its |journal=Integrative and Comparative Biology |language=en |volume=57 |issue=3 |pages=455–466 |doi=10.1093/icb/icx072 |issn=1540-7063}}</ref> Among Ecdysozoa, their nearest relatives may be Kinorhyncha and Loricifera<ref name=":0" />; together, these three groups form the putative Scalidophora clade, named after the spines covering the introvert (scalids).<ref>{{cite journal |author1=Dunn, C. W. |author2=Hejnol, A. |author3=Matus, D. Q. |author4=Pang, K. |author5=Browne, W. E. |author6=Smith, S. A. |author7=Seaver, E. |author8=Rouse, G. W. |author9=Obst, M. | title = Broad Phylogenomic Sampling Improves Resolution of the Animal Tree of Life | journal = Nature | date = 10 April 2008 | volume = 452 | issue = 7188 | pages = 745–749 | doi = 10.1038/nature06614 | pmid = 18322464 | bibcode = 2008Natur.452..745D |s2cid=4397099 }}</ref>

Priapulid-like fossils are known at least as far back as the Middle Cambrian. They were likely major predators of the Cambrian period. However, crown-group priapulids cannot be recognized until the Carboniferous.<ref name="Budd2000">{{cite journal |last1=Budd |first1=G. E. |last2=Jensen |first2=S. |date=May 2000 |title=A critical reappraisal of the fossil record of the bilaterian phyla |volume=75 |issue=2 |pages=253–95 |journal=Biological Reviews of the Cambridge Philosophical Society |doi=10.1111/j.1469-185X.1999.tb00046.x |pmid=10881389|s2cid=39772232 }}</ref> Priapulida appear to have retained some traits of the ancestral Ecdysozoan, leading some authors to describe them as "living fossils".<ref>{{cite journal |last1=Webster |first1=Bonnie L. |last2=Copley |first2=Richard R. |last3=Jenner |first3=Ronald A. |last4=Mackenzie-Dodds |first4=Jacqueline A. |last5=Bourlat |first5=Sarah J. |last6=Rota-Stabelli |first6=Omar |last7=Littlewood |first7=D. T. J. |last8=Telford |first8=Maximilian J. |date=November 2006 |title=Mitogenomics and phylogenomics reveal priapulid worms as extant models of the ancestral Ecdysozoan |journal=Evolution & Development |volume=8 |issue=6 |pages=502–510 |doi=10.1111/j.1525-142x.2006.00123.x |pmid=17073934}}</ref>

==Anatomy== Priapulids are cylindrical worm-like animals, ranging from about 0.2<ref>{{cite book|url=https://books.google.com/books?id=MKUab3WegL0C&q=Tubiluchus+mm&pg=PA29 |title=Multicellular Animals: Order in Nature – System Made by Man|isbn=978-3-540-00146-1|last1=Ax|first1=Peter|date=2003-04-08|publisher=Springer }}</ref> to 39 centimetres<ref>{{cite journal|jstor=3227009|title= Halicryptus higginsi n.sp. (Priapulida): A Giant New Species from Barrow, Alaska |journal= Invertebrate Biology | volume=118 |issue= 4 | pages=404–413|last1= Shirley |first1= Thomas C. |last2= Storch |first2= Volker |year= 1999 |doi= 10.2307/3227009 |bibcode= 1999InvBi.118..404S }}</ref> (0.08 to 15.35 inches) long, with a median anterior mouth quite devoid of any armature or tentacles. They show both radial and bilateral symmetry. The gonads, protonephridia and ventral nerve cord are bilateral, while the introvert, pharynx and brain show radial symmetry, which appears to be a secondary trait.<ref>[https://www.diva-portal.org/smash/get/diva2:172290/FULLTEXT01.pdf Aspects of priapulid development]</ref><ref>{{cite journal | last1=Adrianov | first1=Andrey V. | last2=Malakhov | first2=Vladimir V. | title=Symmetry of priapulids (Priapulida). 1. Symmetry of adults | journal=Journal of Morphology | date=2001 | volume=247 | issue=2 | pages=99–110 | doi=10.1002/1097-4687(200102)247:2<99::AID-JMOR1005>3.0.CO;2-0 | pmid=11223921 | url=https://onlinelibrary.wiley.com/doi/abs/10.1002/1097-4687%28200102%29247%3A2%3C99%3A%3AAID-JMOR1005%3E3.0.CO%3B2-0 | url-access=subscription }}</ref> The larvae also show internal and external characteristics of radial symmetry.<ref>{{cite journal | last1=Adrianov | first1=A. V. | last2=Malakhov | first2=V. V. | title=Symmetry of priapulids (Priapulida). 2. Symmetry of larvae | journal=Journal of Morphology | date=2001 | volume=247 | issue=2 | pages=111–121 | doi=10.1002/1097-4687(200102)247:2<111::AID-JMOR1006>3.0.CO;2-C | pmid=11223922 }}</ref> The adult body is divided into a main trunk or abdomen and a somewhat swollen proboscis region ornamented with longitudinal ridges. In addition, it is ringed and often has circles of spines, which are continued into the slightly protrusible pharynx.<ref name=EB1911/> Family Priapulidae have species with a tail or a pair of caudal appendages. A slender tail or tail filament is also found in family Tubiluchidae. Appendages are absent in the remaining families.<ref>{{Cite journal |last1=Schmidt-Rhaesa |first1=Andreas |last2=Rothe |first2=Birgen H. |last3=Martínez |first3=Alejandro García |date=November 2013 |title=Tubiluchus lemburgi, a new species of meiobenthic Priapulida |url=https://linkinghub.elsevier.com/retrieve/pii/S004452311300051X |journal=Zoologischer Anzeiger - A Journal of Comparative Zoology |language=en |volume=253 |issue=2 |pages=158–163 |doi=10.1016/j.jcz.2013.08.004|bibcode=2013ZooAn.253..158S |url-access=subscription }}</ref><ref>{{Cite book |last1=Margulis |first1=Lynn |url=https://books.google.com/books?id=9IWaqAOGyt4C&dq=Priapulus+Meiopriapulus+Halicryptus+Maccabeus+tails&pg=PA286 |title=Kingdoms and Domains: An Illustrated Guide to the Phyla of Life on Earth |last2=Chapman |first2=Michael J. |date=2009-03-19 |publisher=Academic Press |isbn=978-0-08-092014-6 |language=en}}</ref> The body has a chitinous cuticle that is moulted as the animal grows.<ref name=IZ>{{cite book | author = Barnes, R. D. | year = 1982 | title = Invertebrate Zoology | publisher = Holt-Saunders International | location = Philadelphia, PA | pages = 873–877 | isbn = 978-0-03-056747-6 }}</ref> Members of the family Chaetostephanidae also secrete a gelatinous tube, open in both ends, which they live in.<ref>{{Cite book |last=Schmidt-Rhaesa |first=Andreas |url=https://books.google.com/books?id=NBP4bvxp1loC&q=Maccabeus%2520gelatinous%2520tube&pg=PA173 |title=Handbook of Zoology |date=2012-12-21 |publisher=Walter de Gruyter |isbn=978-3-11-027253-6 |volume=11 |language=en}}</ref>

There is a wide body-cavity, which has no connection with the renal or reproductive organs, so it is not a coelom; it is probably a blood-space or hemocoel.<ref name=EB1911/> There are no vascular or respiratory systems, but the body cavity does contain phagocytic amoebocytes and cells containing the respiratory pigment haemerythrin.<ref name=IZ />

The alimentary canal is straight, consisting of an eversible pharynx, an intestine, and a short rectum. The pharynx is muscular and lined by teeth.<ref name=IZ /> Three of the five extant families have gone through a significant miniaturization, becoming detritivores (Tubiluchidae and Meiopriapulidae) and filter feeders (Chaetostephanidae). The two remaining families of Priapulidae and Halicryptidae are larger carnivores that feed on other animals, although some species also consume detritus as larvae. The shape of the teeth reflect these different lifestyles, and seem to be adapted mainly towards grasping prey or raking detritus from the sediment into the mouth.<ref name="Wernström">{{Cite journal |last1=Wernström |first1=Joel Vikberg |last2=Slater |first2=Ben J. |last3=Sørensen |first3=Martin V. |last4=Crampton |first4=Denise |last5=Altenburger |first5=Andreas |date=2023-08-12 |title=Geometric morphometrics of macro- and meiofaunal priapulid pharyngeal teeth provides a proxy for studying Cambrian "tooth taxa" |journal=Zoomorphology |volume=142 |issue=4 |pages=411–421 |language=en |doi=10.1007/s00435-023-00617-4 |issn=1432-234X|doi-access=free |hdl=10037/30213 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Higgins |first1=Robert P. |last2=Storch |first2=Volker |date=1991 |title=Evidence for Direct Development in Meiopriapulus fijiensis (Priapulida) |url=https://www.jstor.org/stable/3226738 |journal=Transactions of the American Microscopical Society |volume=110 |issue=1 |pages=37–46 |doi=10.2307/3226738 |jstor=3226738 |url-access=subscription }}</ref> The anus is terminal, although in ''Priapulus'' one or two hollow ventral diverticula of the body-wall stretch out behind it.<ref name=EB1911/>

The nervous system consists of a nerve ring around the pharynx and a prominent cord running the length of the body with ganglia and longitudinal and transversal neurites consistent with an orthogonal organisation.<ref name=Rothe2010>{{Cite journal | last1 = Rothe | first1 = B. H. | last2 = Schmidt-Rhaesa | first2 = A. | doi = 10.1111/j.1744-7410.2010.00185.x | title = Structure of the nervous system in ''Tubiluchus troglodytes'' (Priapulida) | journal = Invertebrate Biology | volume = 129 | pages = 39–58 | date = Winter 2010 | issue = 1 | bibcode = 2010InvBi.129...39R }}</ref> The nervous system retains a basiepidermal configuration with a connection to the ectoderm, forming part of the body wall. There are no specialized sense organs, but there are sensory nerve endings in the body, especially on the proboscis.<ref name=IZ />

The priapulids are gonochoristic, having two separate sexes (i.e. male and female).<ref name=pech>{{cite book | last = Pechenik | first = J. A. | title = Biology of the Invertebrates | edition = 6th | year = 2009 | publisher = McGraw-Hill | location = New York | isbn = 978-0-07-302826-2 | page = 454 }}</ref> Their male and female organs are closely associated with the excretory protonephridia. They comprise a pair of branching tufts, each of which opens to the exterior on one side of the anus. The tips of these tufts enclose a flame-cell like those found in flatworms and other animals, and these probably function as excretory organs. As the animals mature, diverticula arise on the tubes of these organs, which develop either spermatozoa or ova. These sex cells pass out through the ducts.<ref name=EB1911>{{EB1911|last=Shipley|first=Arthur Everett|author-link=Arthur Shipley|wstitle=Priapuloidea|volume=22|page=313|inline=1}}</ref> The perigenital area of the genus ''Tubiluchus'' exhibits sexual dimorphism.<ref>{{cite journal| title = A new meiobenthic priapulid (Priapulida, Tubiluchidae) from a Mediterranean submarine cave| year = 2003| doi = 10.1080/11250000309356499| last1 = Todaro| first1 = M. Antonio| last2 = Shirley| first2 = Thomas C.| journal = Italian Journal of Zoology| volume = 70| pages = 79–87| s2cid = 84539380| doi-access = free| hdl = 11380/303453| hdl-access = free}}</ref>

=== Reproduction and development === For the species ''Priapulus caudatus'', the 80 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 bilaterians, has 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>

Stem-group priapulids are known from the Middle Cambrian Burgess Shale, where their soft-part anatomy is preserved, often in conjunction with their gut contents – allowing a reconstruction of their diets.<ref name=Vannier2010>{{cite journal| last1 = Vannier | first1 = J.| last2 = Calandra | first2 = I.| last3 = Gaillard | first3 = C.| last4 = Zylinska | first4 = A. | title = Priapulid worms: Pioneer horizontal burrowers at the Precambrian-Cambrian boundary | journal = Geology | year = 2010 | volume = 38 | issue = 8 | pages = 711–714| doi = 10.1130/G30829.1 | bibcode = 2010Geo....38..711V }}</ref> In addition, isolated microfossils (corresponding to the various teeth and spines that line the pharynx and introvert) are widespread in Cambrian deposits,<ref>{{Cite journal |last1=Slater |first1=Ben J. |last2=Harvey |first2=Thomas H. P. |last3=Guilbaud |first3=Romain |last4=Butterfield |first4=Nicholas J. |date=January 2017 |editor-last=Rahman |editor-first=Imran |title=A cryptic record of Burgess Shale-type diversity from the early Cambrian of Baltica |journal=Palaeontology |language=en |volume=60 |issue=1 |pages=117–140 |doi=10.1111/pala.12273|doi-access=free |bibcode=2017Palgy..60..117S |hdl=2381/38663 |hdl-access=free }}</ref> allowing the distribution of priapulids – and even individual species – to be tracked widely through Cambrian oceans.<ref>{{Cite journal | doi = 10.1111/pala.12168| title = The macro- and microfossil record of the Cambrian priapulid ''Ottoia''| journal = Palaeontology| date = July 2015| volume = 58 | issue = 4 | pages = 705–721|last1 = Smith | first1 = M. R. | last2 = Harvey | first2 = T. H. P. | last3 = Butterfield | first3 = N. J. | url = http://dro.dur.ac.uk/18218/1/18218.pdf| doi-access = free | bibcode = 2015Palgy..58..705S}}</ref><ref name="Wernström"/> Trace fossils that are morphologically almost identical to modern priapulid burrows (''Treptichnus pedum'') officially mark the start of the Cambrian period, suggesting that priapulids, or at least close anatomical relatives, evolved around this time.<ref name=Vannier2010 /> Crown-group priapulid body fossils are first known from the Carboniferous.<ref name=Budd2000 />

==Phylogeny==

=== External phylogeny === {{citation needed|date=January 2024}} {{clade |label1=Ecdysozoa|sublabel1=>529 mya |1={{clade |label1=Scalidophora |1={{clade |1='''Priapulida''' 50px |2=Kinorhyncha 80 px }} |2={{clade |label1=Nematoida |1={{clade |1=Nematoda 70px |2=Nematomorpha 60px }} |label2=Panarthropoda |2={{clade |1=Onychophora 80 px |label2=Tactopoda |2={{clade |1=Tardigrada 60 px |2=Arthropoda 60 px }} }} }} }} }}

=== Internal phylogeny === {{citation needed|date=January 2024}} {{clade| style=font-size:100%;line-height:80% |1={{clade |1=†Archaeopriapulida [paraphyletic] |2=†Ancalagonida Adrianov & Malakhov 1995 |3={{clade |1=†''Markuelia'' Valkov 1983 |2={{clade |1=†Palaeoscolecida Conway Morris & Robinson 1986 |2={{clade |1=Kinorhyncha Reinhard 1887 (Spiny crown worms; Mud dragons) |label2='''Priapulida''' |2={{clade |label1=Meiopriapulomorpha |1={{clade |label1=Tubiluchidae |1={{clade |1=†''Paratubiluchus'' Han et al. 2004 |2=''Meiopriapulus'' Morse 1981 |3=''Tubiluchus'' van der Land 1968 }} }} |label2=Priapulimorpha |2={{clade |label1=Maccabeidae |1=''Maccabeus'' Por 1973 |2={{clade |label1=Halicryptidae |1=''Halicryptus'' von Siebold 1849 |label2=Priapulidae |2={{clade |1={{clade |1=†''Priapulites'' Schram 1973 |2=†''Xiaoheiqingella'' Hu 2002 }} |2={{clade |1=''Priapulopsis'' Koren & Danielssen 1875 |2={{clade |1=''Acanthopriapulus'' van der Land 1970 |2=''Priapulus'' Lamarck 1816 }} }} }} }} }} }} }} }} }} }} }}

==Classification== {{See also|List of bilateral animal orders}}

There are 22 known extant species:<ref>{{cite book| url = https://books.google.com/books?id=YHetDwAAQBAJ&dq=We+follow+here+the+familial+classification+of+Schmidt-Rhaesa+%282013b%29.&pg=PA167| title = The Invertebrate Tree of Life| isbn = 978-0-691-17025-1| last1 = Giribet| first1 = Gonzalo| last2 = Edgecombe| first2 = Gregory D.| date = 3 March 2020| publisher = Princeton University Press}}</ref><ref>[http://www.catalogueoflife.org/annual-checklist/2019/browse/classification/kingdom/Animalia/phylum/Cephalorhyncha/class/Priapulida/fossil/0/match/1 2019 Annual Checklist : Browse taxonomic classification phylum: Cephalorhyncha, class: Priapulida]</ref> [[File:Ottoia reconstruction.jpg|thumb|200px|Illustration of ''Ottoia'', a prehistoric priapulid.]]

Phylum '''Priapulida''' Théel 1906 *Order Halicryptomorpha Salvini-Plawen 1974 [Adrianov & Malakhov 1995; Salvini-Plawen 1974; Eupriapulida Lemburg, 1999] **Family Halicryptidae Salvini-Plawen 1974 ***Genus ''Halicryptus'' ****Species ''H. higginsi'' (Shirley & Storch, 1999) ****Species ''H. spinulosus'' (von Siebold, 1849) *Order Priapulomorpha Adrianov & Malakhov 1995 (assigned its own order by <ref>Adrianov A. V, Malakhov V. V. 2001. Symmetry of priapulids (Priapulida). 1. Symmetry of adults. 247:99–110.</ref>) **Family Priapulidae Gosse 1855 [Xiaoheiqingidae (sic) Hu 2002] ***Genus ''Acanthopriapulus'' ****Species ''A. horridus'' (Théel, 1911) ***Genus ''Priapulopsis'' ****Species ''P. australis'' (de Guerne, 1886) ****Species ''P. bicaudatus'' (Danielssen, 1869) ****Species ''P. cnidephorus'' (Salvini-Plawen, 1973) ***Genus ''Priapulus'' ****Species ''P. abyssorum'' (Menzies, 1959) ****Species ''P. caudatus'' (Lamarck, 1816) ****Species ''P. tuberculatospinosus'' (Baird, 1868) **Family Tubiluchidae van der Land 1970 [Meiopriapulidae Adrianov & Malakhov 1995] ***Genus ''Tubiluchus'' ****Species ''T. arcticus'' (Adrianov, Malakhov, Tchesunov & Tzetlin, 1989) ****Species ''T. australensis'' (van der Land, 1985) ****Species ''T. corallicola'' (van der Land, 1968) ****Species ''T. lemburgi'' (Schmidt-Rhaesa, Rothe & Martínez, 2013) ****Species ''T. pardosi'' (Schmidt-Rhaesa, Panpeng & Yamasaki, 2017) ****Species ''T. philippinensis'' (van der Land, 1985) ****Species ''T. remanei'' (van der Land, 1982) ****Species ''T. soyoae'' (Schmidt-Rhaesa, Panpeng & Yamasaki, 2017) ****Species ''T. troglodytes'' (Todaro & Shirley, 2003) ****Species ''T. vanuatensis'' (Adrianov & Malakhov, 1991) **Genus ''Meiopriapulus'' ***Species ''M. fijiensis'' (Morse, 1981) *Order Seticoronaria **Family Chaetostephanidae Por & Bromley 1974 [Chaetostephanidae Salvini-Plawen 1974] ***Genus ''Maccabeus'' ****Species ''M. cirratus'' (Malakhov, 1979) ****Species ''M. tentaculatus'' (Por, 1973)

===Extinct groups=== Stem-group †'''Scalidophora''' *Order †Ancalagonida Adrianov & Malakhov 1995 [Fieldiida Adrianov & Malakhov 1995] **Family †Ancalagonidae Conway Morris 1977 ***Genus †''Ancalagon'' Conway Morris 1977 **Family †Fieldiidae Conway Morris 1977 ***Genus †''Fieldia'' Walcott 1912

Stem-group †'''Palaeoscolecida''' *Family †Selkirkiidae Conway Morris 1977 **Genus †''Selkirkia'' Walcott 1911 non Hemsley 1884 *Order †Ottoiomorpha Adrianov & Malakhov 1995 **Genus †''Scolecofurca'' Conway Morris 1977 **Family †Ottoiidae Walcott 1911 ***Genus †''Ottoia'' Walcott 1911 **Family †Corynetidae Huang, Vannier & Chen 2004 ***Genus †''Corynetis'' Luo & Hu 1999 [''Anningvermis'' Huang, Vannier & Chen 2004] **Family †Miskoiidae Walcott 1911 ***Genus †''Miskoia'' Walcott 1911 ***Genus †''Louisella'' Conway Morris 1977

== References == {{Reflist}}

== External links == {{Wikispecies|Priapulida}} * {{cite news | publisher = University of Bristol | url = http://www.bris.ac.uk/news/2006/1052.html | title = Evolution of the penis worm | work = Press Releases | date = 2006-08-09 }}

Category:Priapulida Category:Ecdysozoa phyla Category:Extant Pennsylvanian first appearances