Editing Echinoderm (section)

====Internal phylogeny: total group====

The lack of a consensus [[cladistic]] phylogeny incorporating extinct echinoderm groups has resulted in the continued use of terms from [[Linnaean taxonomy|Linnaean taxonomies]], even when the named taxa are known to be [[paraphyletic]] and/or [[polyphyletic]].

=====Linnaean taxonomies=====

Three taxonomies introduced nearly all of the traditional subphyla and class divisions that continue to be referenced in cladistic work:

* [[Francis Arthur Bather|F. A. Bather]] produced the earliest widely referenced classification of both fossil and extant echinoderms in 1900, using a two-subphylum system.<ref>{{harvnb|Smith|1984|pp=433–434}}</ref>
* In 1966, the ''[[Treatise on Invertebrate Paleontology]]'', rejected Bather's classification, replacing it with a new four-subphylum scheme<ref>{{harvnb|Moore|1966|pp=U2–U3}}</ref> that had been previously proposed by [[Barry Fell|H. B. Fell]].<ref>{{harvnb|Sprinkle|1973|p=3}}</ref>
* James Sprinkle which added a fifth subphylum to the ''Treatise'' taxonomy in 1973.<ref>{{harvnb|Sprinkle|1973}}</ref>  His later class-level taxonomy of the five subphyla was the most recent approach cited in an early cladistic re-assessment of the phylum.<ref>{{harvnb|Smith|1984|p=436}}</ref>

{| class="wikitable"
|+Notable Linnaean taxonomies of the phylum Echinodermata
! Bather, 1900<ref>{{harvnb|Bather|1900}}</ref>
! Moore (ed.), 1966–7<ref>{{harvnb|Moore|1966}}</ref><ref>{{harvnb|Ubaghs|1967}}</ref>
! Sprinkle, 1980<ref>{{harvnb|Sprinkle|1980a}}</ref><ref>{{harvnb|Sprinkle|1980b}}</ref>
|- style="vertical-align:top;"
|
* ''Phylum'' '''Echinoderma''' {{small|Latreille, 1825<ref>{{harvnb|Ubaghs|1967|p=S5|loc=footnote 1}}</ref>}}
** ''Subphylum'' [[Pelmatozoa]] {{small|Leuckart,&nbsp;1848}}
*** ''Class'' Cystidea† {{small|von&nbsp;Buch,&nbsp;1844}}
*** ''Class'' [[Blastoidea]]† {{small|Say,&nbsp;1825 ''sensu extenso''}}
*** ''Class'' [[Crinoidea]] {{small|Miller,&nbsp;1821}}
*** ''Class'' [[Edrioasteroidea]]† {{small|E.&nbsp;Billings,&nbsp;1854–58; Huxley,&nbsp;1877; Bather,&nbsp;1899}}
** ''Subphylum'' [[Eleutherozoa]] {{small|Bell, 1891}}
*** ''Class'' [[Holothuroidea]] {{small|C.&nbsp;T.&nbsp;v.&nbsp;Siebold,&nbsp;1848}}
*** ''Class'' [[Stelleroidea]] {{small|Gregory, 1900}}
*** ''Class'' [[Echinoidea]] {{small|[[Leske]], 1778}}
|
* ''Phylum'' '''Echinodermata''' {{small|Klein,&nbsp;1734; Brugière, 1789}}
** ''Subphylum'' [[Homalozoa]]† {{small|Whitehouse,&nbsp;1941}}
*** ''Class'' [[Stylophora]]† {{small|Gill&nbsp;&&nbsp;Caster,&nbsp;1960}}
*** ''Class'' [[Homostelea]]† {{small|Gill&nbsp;&&nbsp;Caster,&nbsp;1960}}
*** ''Class'' [[Homoiostelea]]† {{small|Gill&nbsp;&&nbsp;Caster,&nbsp;1960}}
** ''Subphylum'' [[Crinozoa]] {{small|Matsumoto,&nbsp;1929}}
*** ''Class'' [[Lepidocystis|Lepidocystoidea]]† {{small|Durham,&nbsp;1967}}
*** ''Class'' [[Eocrinoidea]]† {{small|Jaekel,&nbsp;1918}}
*** ''Class'' [[Cystoidea]]† {{small|von&nbsp;Buch,&nbsp;1846}}
*** ''Class'' Edrioblastoidea† {{small|Fay,&nbsp;1962}}
*** ''Class'' Parablastoidea† {{small|Hudson,&nbsp;1907}}
*** ''Class'' [[Blastoidea]]† {{small|Say,&nbsp;1825}}
*** ''Class'' [[Paracrinoidea]]† {{small|Regnéll,&nbsp;1945}}
*** ''Class'' [[Crinoidea]] {{small|Miller,&nbsp;1821}}
** ''Subphylum'' [[Asterozoa]] {{small|Zittel&nbsp;1895}}
*** ''Class'' [[Stelleroidea]] {{small|Lamarck&nbsp;1816}}
** ''Subphylum'' [[Echinozoa]] {{small|Haekel&nbsp; Zittel&nbsp;1895}}
*** ''Class'' [[Helicoplacoidea]]† {{small|Durham&nbsp;&&nbsp;Caster,&nbsp;1963}}
*** ''Class'' [[Camptostroma|Camptostromatoidea]]† {{small|Durham,&nbsp;1966}}
*** ''Class'' [[Edrioasteroidea]]† {{small|Billings,&nbsp;1858}}
*** ''Class'' Cyclocystoidea† {{small|Miller&nbsp;&&nbsp;Gurley,&nbsp;1895}}
*** ''Class'' [[Ophiocistioidea]]† {{small|Solas,&nbsp;1899}}
*** ''Class'' [[Echinoidea]] {{small|Leske,&nbsp;1778}}
*** ''Class'' [[Holothuroidea]] {{small|de&nbsp;Blainville,&nbsp;1834}}
|
* ''Phylum'' '''Echinodermata''' {{small|de Bruguière ''[sic]'',&nbsp;1791}}
** ''Subphylum'' [[Homalozoa]]† {{small|Whitehouse,&nbsp;1941}}
*** ''Class'' [[Ctenocystoidea]]† {{small|Robinson&nbsp;& Sprinkle,&nbsp;1969}}
*** ''Class'' [[Stylophora]]† {{small|Gill&nbsp;&&nbsp;Caster,&nbsp;1960}}
*** ''Class'' [[Homostelea]]† {{small|Gill&nbsp;&&nbsp;Caster,&nbsp;1960}}
*** ''Class'' [[Homoiostelea]]† {{small|Gill&nbsp;&&nbsp;Caster,&nbsp;1960}}
** ''Subphylum'' [[Blastozoa]]† {{small|Sprinkle,&nbsp;1973}}
*** ''Class'' [[Eocrinoidea]]† {{small|Jaekel,&nbsp;1918}}
*** ''Class'' [[Rhombifera]]† {{small|Zittel,&nbsp;1879}}
*** ''Class'' [[Diploporita]]† {{small|Müller,&nbsp;1854}}
*** ''Class'' Parablastoidea† {{small|Hudson,&nbsp;1907}}
*** ''Class'' [[Blastoidea]]† {{small|Say,&nbsp;1825}}
** ''Subphylum'' [[Crinozoa]] {{small|Matsumoto,&nbsp;1929, restricted&nbsp;in Sprinkle,&nbsp;1973}}
*** ''Class'' [[Paracrinoidea]]† {{small|Regnéll,&nbsp;1945}}
*** ''Class'' [[Crinoidea]] {{small|Miller,&nbsp;1821}}
** ''Subphylum'' [[Asterozoa]] {{small|Zittel&nbsp;1895}}
*** ''Class'' [[Asteroidea]] {{small|de&nbsp;Blainville,&nbsp;1830}}
*** ''Class'' [[Ophiuroidea]] {{small|Gray,&nbsp;1840}}
** ''Subphylum'' [[Echinozoa]] {{small|Haekel&nbsp; Zittel&nbsp;1895}}
*** ''Class'' [[Helicoplacoidea]]† {{small|Durham&nbsp;&&nbsp;Caster,&nbsp;1963}}
*** ''Class'' [[Edrioasteroidea]]† {{small|Billings,&nbsp;1858}}
*** ''Class'' Edrioblastoidea† {{small|Fay,&nbsp;1962}}
*** ''Class'' Cyclocystoidea† {{small|Miller&nbsp;&&nbsp;Gurley,&nbsp;1895}}
*** ''Class'' [[Ophiocistioidea]]† {{small|Solas,&nbsp;1899}}
*** ''Class'' [[Echinoidea]] {{small|Leske,&nbsp;1778}}
*** ''Class'' [[Holothuroidea]] {{small|de&nbsp;Blainville,&nbsp;1834}}
|}


Other proposed classes not included at that rank in any of the above taxonomies include:

* [[Eleutherozoa#Asterozoa vs Cryptosyringida|Cryptosyringida]] {{small|Smith, 1984}}<ref>{{harvnb|Smith|1984|pp=436–439, 453–454}}</ref>
* [[Somasteroidea]] {{small|Spencer, 1951}}<ref>{{harvnb|PBDB Somasteroidea}}</ref> 
* [[Asterozoa#Stenuroidea|Stenuroidea]] {{small|Spencer, 1951}}<ref>{{harvnb|PBDB Stenuroidea}}</ref>
* Coronoidea {{small|Brett et al., 1983}}<ref>{{harvnb|PBDB Coronoidea}}</ref>
* [[Concentricycloidea]] {{small|Baker, Rowe & Clark, 1986}}<ref>{{harvnb|Rowe|Baker|Clark|1988}}</ref>

There are also several common alternative names involving homalozoans:

* [[Carpoidea]] {{small|Jaekel, 1900}} for Homalozoa, giving rise to the term "carpoids"<ref>{{harvnb|Rahman|2009}}</ref>
* [[Cincta]] {{small|Jaekel, 1918}} as either the senior synonym of or sole order within Homostelea<ref name=Rozhnov2022>{{harvnb|Rozhnov|2022|p=1310}}</ref>
* [[Soluta (echinoderm)|Soluta]] {{small|Jaekel, 1901}} as either the senior synonym of or sole order within Homoiostelea<ref name=Rozhnov2022 />
* Calcichordata {{small|Jeffries, 1967}}, a subphylum effectively identical to Stylophora that was central<ref>{{harvnb|Gee|1996|p=223}}</ref> to the now-disproven<ref>{{harvnb|Lefebvre|Guensburg|Martin|Mooi|2019}}</ref> [[calcichordate hypothesis]]

=====Cladograms=====

According to 2024 review, there are two main schools of thought regarding echinoderm phylogeny:  One that sees pentaradiality as a [[plesiomorphic]] trait of the phylum, and another that considers it a derived trait ([[apomorphy]]).<ref>{{harvnb|Rahman|Zamora|2024|p=308}}</ref>

Note that neither cladogram shown below includes all of the traditional classes, or even all of the classes mentioned in accompanying text.

; Pentaradiality as a plesiomorphy

Supporters of pentaradiality as an initial condition of the phylum note that radial forms are the first uncontested echinoderms to appear in the fossil record. They also define homologies of echinoderm anatomy based on a division of the skeleton into two parts: those that are or are not associated with the water vascular system.<ref name=twoclades />

The following cladogram is based on David & Mooi (1999)<ref>{{harvnb|David|Mooi|1999|p=100}}</ref> and David, Lefebvre, Mooi, and Parsley (2000):<ref>{{harvnb|David|Lefebvre|Mooi|Parsley|2000|p=549}}</ref>

{{Clade
|label1='''Echinodermata'''
|sublabel1={{small|([[total group]])}}
|1={{Clade
   |1=? ''[[Arkarua]]''† [[File:Arkarua adami pennetta.png|60px]]
   |2={{Clade
      |1=[[Helicoplacoidea]]† [[File:Helicoplacus-cropped.png|20px]]
      |2=[[Edrioasteroidea]]† [[File:Foerstediscus-splendens.png|30px]]
      |3={{Clade
         |label1=[[Blastozoa]]†
         |1={{Clade
            |grouplabel1={{Clade labels |top1=30% |color1=indigo |label1="[[Eocrinoidea]]"† }}
            |1=[[Lepidocystis|Lepidocystiodea]]† [[File:Kinzercystis durhami.svg|20px]]|barbegin1=indigo
            |2={{Clade
               |1=some Eocrinoids† [[File:Gogia-cropped.png|40px]] |bar1=indigo
               |2={{Clade
                  |1={{Clade
                     |1=some Eocrinoids† |bar1=indigo
                     |2={{Clade
                        |1=some Eocrinoids† |barend1=indigo
                        |2={{Clade
                           |1=[[Homostelea]]† {{small|(Cincta)}} [[File:Protcinctus-cropped.png|35px]]
                           |2=[[Ctenocystoidea]]† [[File:Ctenocystis-cropped.png|35px]]
                        }}
                     }}
                     |3=[[Homoiostelea]]† {{small|(Soluta)}} [[File:Coleicarpus-cropped.png|15px]]
                     |4={{Clade
                        |grouplabel1={{Clade labels |top1=30% |color1=indigo |label1="[[Cystoidea]]"† }}
                        |1=[[Diploporita]]† |barbegin1=indigo
                        |2={{Clade
                           |1=[[Rhombifera]]† |barend1=indigo
                           |2=[[Blastoidea]]†
                        }}
                     }}
                  }}
               }}
            }}
         }}
         |label2='''Echinodermata'''
         |sublabel2={{small|([[crown group]])}}
         |2={{Clade
            |label1=[[Crinozoa]]
            |1={{Clade
               |1=[[Crinoidea]] [[File:202012 Metacrinus rotundus.svg|40px]]
               |2=[[Stylophora]]† [[File:Ceratocystis-cropped.png|50px|]]
            }}
            |label2=[[Eleutherozoa]]
            |2={{Clade
               |label1=[[Asterozoa]]
               |1={{Clade
                  |1=[[Ophiuroidea]] [[File:Ophiocoma (26150611418).jpg|60px]]
                  |2=[[Asteroidea]] [[File:Echinaster serpentarius (USNM E28192) 001.png|50px]]
               }}
               |label2=[[Echinozoa]]
               |2={{Clade
                  |1=[[Echinoidea]] [[File:Echinometra viridis.png|50px]]
                  |2={{Clade
                     |1=[[Ophiocistioidea]]† [[File:Sollasina-cthulu-cropped.png|50px]]
                     |2=[[Holothuroidea]] [[File:Holothuria parvula.png|60px]]
                  }}
               }}
            }}
         }}
      }}
   }}
}}
}}

In this theory, the controversial<ref name=arkarua>{{harvnb|Rahman|Zamora|2024|p=300}}</ref> [[Ediacaran]] fossil ''[[Arkarua]]'' is tentatively placed as the sister to all other echinoderms.  [[Helicoplacoidea]] and [[Edrioasteroidea]] join it in the stem group. [[Pelmatozoa]], [[Eocrinoidea]], and [[Cystoidea]] are shown to be paraphyletic while [[Homalozoa]] is polyphyletic.

; Pentaradiality as an apomorphy

Those who find pentaradiality to be derived incorporate the recently-discovered fossils ''[[Ctenoimbricata]]'' (seen as a possible sister to all other echinoderms) and ''[[Helicocystis]]'' (seen as bridging the triradial helicoplacoids and the pentaradial crown group). They cite research indicating that the early appearance of pentaradial forms is likely due to an incomplete fossil record, as well as multiple studies showing non-radial forms as an early stem group, to argue that this is phylogeny represents an emerging consensus.<ref name=twoclades />  They reject ''Arkarua'' as an echinoderm due to its lack of [[stereom]] and possession of true pentaradiality instead of the 2-1-2 pseudo-pentaradiality seen in all early forms.<ref name=arkarua />

The following cladogram is based on Rahman & Zamora (2024),<ref>{{harvnb|Rahman|Zamora|2024|p=310}}</ref> incorporating class<ref>{{harvnb|Rahman|Zamora|2024|p=311}}</ref> and subphylum<ref>{{harvnb|Rahman|Zamora|2024|p=298}}</ref> names from the text:

{{Clade
   |label1='''Echinodermata'''
   |sublabel1={{small|([[total group]])}}
   |1={{Clade
         |label1=
         |1=''[[Ctenoimbricata]]''† [[File:Ctenoimbricata-cropped.png|35px]]
         |grouplabel2={{Clade labels |top1=20% |bar1=indigo |label1="Homalozoa"†}}
         |2={{Clade
            |1=''Ctenocystis''† [[File:Ctenocystis-cropped.png|35px]] {{small|(a [[Ctenocystoidea|Ctenocystoid]]†)}}
            |2=''Courtessolea''† [[File:Courtessolea-cropped.png|35px]] {{small|(a [[Ctenocystoidea|Ctenocystoid]]†)}}
         }}
         |barbegin2=indigo
         |3={{Clade
            |label1=
            |1=''[[Protocinctus]]''† [[File:Protcinctus-cropped.png|35px]] {{small|(a [[Cinctan]]† a.k.a. Homostelean†)}}
            |bar1=indigo
            |2={{Clade
               |label1=
               |1={{Clade
                  |label1=
                  |1=''Coleicarpus''† [[File:Coleicarpus-cropped.png|15px]] {{small|(a [[Soluta (echinoderm)|Solute]]† a.k.a. Homoiostelean†)}}
                  |2=? ''Ceratocystis''† [[File:Ceratocystis-cropped.png|50px|]] {{small|(a [[Stylophoran]]†)}} |state2=dashed
               }}
               |barend1=indigo
               |2={{Clade
                  |label1=
                  |1=''[[Helicoplacus]]''† [[File:Helicoplacus-cropped.png|20px]] {{small|(a [[Helicoplacoid]]†)}}
                  |2={{Clade
                     |1=''[[Helicocystis]]''† [[File:Helicocystis-cropped.png|15px]]
                     |label2='''Echinodermata'''
                     |sublabel2={{small|([[crown group]])}}
                     |2={{Clade
                        |label1=
                        |1=''[[Gogia]]''† [[File:Gogia-cropped.png|40px]] {{small|(an&nbsp;[[Eocrinoid]]†)}}
                        |2=''[[Camptostroma]]''† [[File:Camptostroma-cropped.png|30px]] {{small|(an&nbsp;[[Edrioasteroid]]†)}}
                        |3=[[Crinoidea]] [[File:202012 Metacrinus rotundus.svg|40px]]
                        |label4=[[Eleutherozoa]]
                        |4={{Clade
                           |label1=[[Echinozoa]]
                           |1={{Clade
                              |1=[[Echinoidea]] [[File:Echinometra viridis.png|50px]]
                              |2=[[Holothuroidea]] [[File:Holothuria parvula.png|60px]]
                           }}
                           |label2=[[Asterozoa]]
                           |2={{Clade
                              |1=[[Asteroidea]] [[File:Echinaster serpentarius (USNM E28192) 001.png|50px]]
                              |2=[[Ophiuroidea]] [[File:Ophiocoma (26150611418).jpg|60px]]
}} }} }} }} }} }} }} }} }}

Here, [[Homalozoa]] (with uncertain placement of [[Stylophora]]) is shown to be a paraphyletic assemblage along the stem group, followed by [[Helicoplacoidea]] and then ''[[Helicocystis]]'' as the sister of the crown group.  The details of [[Blastozoa]] vs [[Crinozoa]] are not addressed, as they are represented only by the classes [[Eocrinoidea]] and [[Crinoidea]], respectively, and the overall nature of [[Pelmatozoa]] remains unresolved.  The four-way [[polytomy]] including the [[Eleutherozoa]] and [[Crinoidea]] shows either ''[[Camptostroma]]'' or ''[[Gogia]]'' or both could prove to be outside of the crown group.