Editing Sea spider (section)

===Interrelationship===
{{cladogram
|title=
|align= right
|caption= Internal phylogeny of Pycnogonida.<ref name=":0" /><ref name=":14" />
|cladogram=
{{clade| style=width:35em;font-size:90%;line-height:100%
|1={{clade
|state1=double|label1=?|1=stem-groups (e.g. ''[[Palaeoisopus]]'',  ''[[Flagellopantopus]]'', ''[[Palaeopantopus]]'')
|label2=Pantopoda|2={{clade
 |label1=Stiripasterida|1=[[Austrodecidae]]
 |label2=Eupantopodida|2={{clade
  |1={{clade
  |label1=Colossendeoidea|1={{clade
  |1=[[Colossendeidae]]
  |2={{clade
   |1=[[Rhynchothoracidae]] 
   |2=[[Pycnogonidae]]
}} }} }}
   |2={{clade
    |1={{clade
     |label1=Phoxichilidioidea|1={{clade
      |1=[[Endeidae]] 
      |2=[[Phoxichilidiidae]]
}}
     |label2=Ammotheoidea|2={{clade
      |1=[[Pallenopsidae]]
      |2=[[Ammotheidae]]
}} }}
    |label2=?|2=[[Ascorhynchidae]]<br>(including ''[[Nymphonella]]''?)
      |3={{clade|label1=Nymphonoidea|1={{clade
       |state1=double|1=[[Callipallenidae]]<br>([[paraphyletic]])
       |2=[[Nymphonidae]]
}} }} }} }} }} }} }} }}
The class Pycnogonida comprises over 1,300 [[species]], which are split into over 80 [[Genus|genera]]. All extant genera are considered part of the single [[Order (biology)|order]] Pantopoda, which was subdivided into 11 [[family (biology)|families]]. Historically there are only 9 families, with species of nowadays Ascorhynchidae placed under Ammotheidae and Pallenopsidae under Callipallenidae. Both were eventually separated after they are considered distinct from the once-belonged families.<ref name=":8" />

Phylogenomic analysis of extant sea spiders was able to establish a backbone tree for Pantopoda, revealing some consistent relationship such as the basal position of [[Austrodecidae]], [[monophyly]] of some major branches (later redefined as superfamilies<ref name=":14">{{Cite journal |last1=Sabroux |first1=Romain |last2=Corbari |first2=Laure |last3=Hassanin |first3=Alexandre |date=2023-05-01 |title=Phylogeny of sea spiders (Arthropoda: Pycnogonida) inferred from mitochondrial genome and 18S ribosomal RNA gene sequences |url=https://www.sciencedirect.com/science/article/abs/pii/S105579032300026X |journal=Molecular Phylogenetics and Evolution |volume=182 |pages=107726 |doi=10.1016/j.ympev.2023.107726 |bibcode=2023MolPE.18207726S |issn=1055-7903}}</ref>) and the [[paraphyly]] of [[Callipallenidae]] in respect to [[Nymphonidae]].<ref name=":8" /><ref>{{Cite journal |last=Hassanin |first=Alexandre |date=2010-01-01 |title=Studying Sources of Incongruence In Arthropod Molecular Phylogenies: Sea Spiders (Pycnogonida) As a Case Study |url=https://www.academia.edu/458876 |journal=Comptes Rendus Biologies}}</ref><ref name=":0">{{Cite journal |last1=Ballesteros |first1=Jesús A |last2=Setton |first2=Emily V W |last3=Santibáñez-López |first3=Carlos E |last4=Arango |first4=Claudia P |last5=Brenneis |first5=Georg |last6=Brix |first6=Saskia |last7=Corbett |first7=Kevin F |last8=Cano-Sánchez |first8=Esperanza |last9=Dandouch |first9=Merai |last10=Dilly |first10=Geoffrey F |last11=Eleaume |first11=Marc P |last12=Gainett |first12=Guilherme |last13=Gallut |first13=Cyril |last14=McAtee |first14=Sean |last15=McIntyre |first15=Lauren |date=2021-01-23 |editor-last=Crandall |editor-first=Keith |title=Phylogenomic Resolution of Sea Spider Diversification through Integration of Multiple Data Classes |url=https://academic.oup.com/mbe/article/38/2/686/5904272 |journal=Molecular Biology and Evolution |language=en |volume=38 |issue=2 |pages=686–701 |doi=10.1093/molbev/msaa228 |issn=1537-1719 |pmc=7826184 |pmid=32915961}}</ref> The topology also suggest Pantopoda undergoing [[convergent evolution|multiple times]] of cephalic appendage reduction/reappearance and polymerous species acquisition, contray to previous hypothesis on pantopod evolution (cephalic appendages were thought to be progressively reduced along the branches, and polymerus condition were though to be ancestral).<ref name=":14" /> On the other hand, the position of [[Ascorhynchidae]] and ''[[Nymphonella]]'' are less certain across multiple results.<ref name=":0" /><ref name=":14" />

The position of Paleozoic pycnogonids are poorly examined, but most, if not, all of them most likely represent members of [[stem-group]] basal than Pantopoda ([[crown-group]] Pycnogonida), especially those with segmented abdomen, a feature that was most likely [[Plesiomorphy and symplesiomorphy|ancestral]] and reduce in the Pantopoda lineage.<ref name=":92">{{Cite journal |last1=Bergström |first1=Jan |last2=Stürmer |first2=Wilhelm |last3=Winter |first3=Gerhard |date=1980 |title=''Palaeoisopus'', ''Palaeopantopus'' and ''Palaeothea'', pycnogonid arthropods from the Lower Devonian Hunsriick Slate, West Germany |url=https://www.academia.edu/5146832 |journal=Paläontologische Zeitschrift |volume=54 |issue=1–2 |pages=7 |doi=10.1007/BF02985882 |bibcode=1980PalZ...54....7B |issn=0031-0220}}</ref><ref name=":19" /><ref>{{Cite journal |last1=Kühl |first1=Gabriele |last2=Poschmann |first2=Markus |last3=Rust |first3=Jes |date=2013 |title=A ten-legged sea spider (Arthropoda: Pycnogonida) from the Lower Devonian Hunsrück Slate (Germany) |url=https://www.cambridge.org/core/journals/geological-magazine/article/abs/tenlegged-sea-spider-arthropoda-pycnogonida-from-the-lower-devonian-hunsruck-slate-germany/49C52AA72ABDF4B6E8DF2F572C0D51AE |journal=Geological Magazine |language=en |volume=150 |issue=3 |pages=556–564 |doi=10.1017/S0016756812001033 |bibcode=2013GeoM..150..556K |issn=0016-7568|url-access=subscription }}</ref><ref name=":14" /><ref name=":1" /> While some phylogenetic analysis placing them within Pantopoda, this result is questionable as they have low support values and based on outdated interpretation of the fossil taxa.<ref name=":12" /><ref name=":20">{{Cite journal |last1=Siveter |first1=Derek J. |last2=Sabroux |first2=Romain |last3=Briggs |first3=Derek E. G. |last4=Siveter |first4=David J. |last5=Sutton |first5=Mark D. |date=2023 |title=Newly discovered morphology of the Silurian sea spider ''Haliestes'' and its implications |url=https://onlinelibrary.wiley.com/doi/10.1002/spp2.1528 |journal=Papers in Palaeontology |language=en |volume=9 |issue=5 |doi=10.1002/spp2.1528 |bibcode=2023PPal....9E1528S |issn=2056-2799|hdl=1983/267d44cb-bd22-4a1d-9d00-b3916c453784 |hdl-access=free }}</ref><ref name=":15">{{Cite journal |last1=Sabroux |first1=Romain |last2=Garwood |first2=Russell J. |last3=Pisani |first3=Davide |last4=Donoghue |first4=Philip C. J. |last5=Edgecombe |first5=Gregory D. |date=2024-10-14 |title=New insights into the Devonian sea spiders of the Hunsrück Slate (Arthropoda: Pycnogonida) |journal=PeerJ |language=en |volume=12 |pages=e17766 |doi=10.7717/peerj.17766 |doi-access=free |pmid=39421419 |pmc=11485130 |issn=2167-8359}}</ref>

According to the [[World Register of Marine Species]], the Class Pycnogonida is subdivided as follows<ref>{{Cite web |title=WoRMS - World Register of Marine Species - Pycnogonida |url=https://marinespecies.org/aphia.php?p=taxdetails&id=1302 |access-date=2024-12-15 |website=marinespecies.org}}</ref> (with subsequent updates on fossil taxa after Sabroux et al. (2023,<ref name=":13" /> 2024<ref name=":1" />)):

*Genus †''[[Cambropycnogon]]'' Waloszek & Dunlop, 2002<ref name=":18" />
*Genus †''[[Flagellopantopus]]'' Poschmann & Dunlop, 2005 (classified under Pantopoda ''incertae sedis'' by WoRMS<ref name=":23" />)
*Genus †''[[Haliestes]]'' Siveter et al., 2004 (previously classified under Order Nectopantpoda Bamber, 2007 and Family Haliestidae Bamber, 2007)
*Genus †''[[Palaeoisopus]]'' Broili, 1928 (Previously classified under Order Palaeoisopoda Hedgpeth, 1978 and Family Palaeoisopodidae Dubinin, 1957)
*Genus †''[[Palaeomarachne]]'' Rudkin et al., 2013
*Genus †''[[Palaeopantopus]]'' Broili, 1929 (Previously classified under Order Palaeopantopoda Broili, 1930 and Family Palaeopantopodidae Hedgpeth, 1955)
* Genus †''[[Palaeothea]]'' Bergstrom, Sturmer & Winter, 1980 (previously classified under Pantopoda, potential ''[[nomen dubium]]'')
* Genus †''[[Pentapantopus]]'' Kühl, Poschmann & Rust, 2013 (previously classified under Pantopoda)
*Order Pantopoda Gerstäcker, 1863<ref>{{Cite web |title=WoRMS - World Register of Marine Species - Pantopoda |url=https://marinespecies.org/aphia.php?p=taxdetails&id=1358 |access-date=2024-12-15 |website=marinespecies.org}}</ref>
**Suborder [[Eupantopodida]] Fry, 1978<ref>{{Cite web |title=WoRMS - World Register of Marine Species - Eupantopodida |url=https://marinespecies.org/aphia.php?p=taxdetails&id=379601 |access-date=2024-12-15 |website=marinespecies.org}}</ref>
***Superfamily [[Ammotheoidea]] Dohrn, 1881
****Family [[Ammotheidae]] Dohrn, 1881
****Family [[Pallenopsidae]] Fry, 1978
***Superfamily [[Ascorhynchoidea]] Pocock, 1904
****Family [[Ascorhynchidae]] Hoek, 1881 (=Eurycydidae Sars, 1891)
***Superfamily [[Colossendeoidea]] Hoek, 1881 (=Pycnogonoidea Pocock, 1904; Rhynchothoracoidea Fry, 1978)
****Family [[Colossendeidae]] Jarzynsky, 1870
****Family [[Pycnogonidae]] Wilson, 1878
****Family [[Rhynchothoracidae]] Thompson, 1909
***Superfamily [[Nymphonoidea]] Pocock, 1904
****Family [[Callipallenidae]] Hilton, 1942
****Family [[Nymphonidae]] Wilson, 1878
***Superfamily [[Phoxichilidioidea]] Sars, 1891
****Family [[Endeidae]] Norman, 1908
****Family [[Phoxichilidiidae]] Sars, 1891
**Suborder [[Stiripasterida]] Fry, 1978<ref>{{Cite web |title=WoRMS - World Register of Marine Species - Stiripasterida |url=https://marinespecies.org/aphia.php?p=taxdetails&id=379600 |access-date=2024-12-05 |website=marinespecies.org}}</ref>
***Family [[Austrodecidae]] Stock, 1954
**Suborder ''incertae sedis''<ref name=":23">{{Cite web |title=WoRMS - World Register of Marine Species - Pantopoda ''incertae sedis'' |url=https://marinespecies.org/aphia.php?p=taxdetails&id=150518 |access-date=2024-12-15 |website=marinespecies.org}}</ref>
*** Family †[[Palaeopycnogonididae]] Sabroux, Edgecombe, Pisani & Garwood, 2023
***Genus ''[[Alcynous]]'' Costa, 1861 (nomen dubium)
***Genus ''[[Foxichilus]]'' Costa, 1836 (nomen dubium)
***Genus ''[[Oiceobathys]]'' Hesse, 1867 (nomen dubium)
***Genus ''[[Oomerus]]'' Hesse, 1874 (nomen dubium)
***Genus ''[[Paritoca]]'' Philippi, 1842 (nomen dubium)
***Genus ''[[Pephredro]]'' Goodsir, 1842 (nomen dubium)
***Genus ''[[Phanodemus]]'' Costa, 1836 (nomen dubium)
***Genus ''[[Platychelus]]'' Costa, 1861 (nomen dubium)