<==o Diplacanthida Berg, 1940 [Diplacanthiformes Berg, 1940]
   |?- †Uraniacanthus spinosus
   |--o †Culmacanthidae
   |  `--o †Culmacanthus Long, 1983
   |     |-- †C. pambulensis Young, 1989b
   |     `-- †C. stewarti
   |--o †Tetanopsyridae
   |  `--o †Tetanopsyrus Gagnier et al., 1999; L. Dev. NNA.
   |     |-- †T. lindoei Gagnier et al., 1999
   |     `-- †T. breviacanthis Hanke, Davis & Wilson, 2001
   `--o †Diplacanthidae Woodward, 1891
      |--o †Diplacanthus Agassiz, 1844 [Rhadinacanthus] M. Dev. Eu. EEu. U. Dev. NA.
      |  |-- †D. longispinus Agassiz, 1844
      |  |-- †D. crassissimus Duff, 1842
      |  |-- †D. tenuistriatus
      |  |-- †D. ellsi
      |  |-- †D. horridus Woodward, 1892
      |  |-- †D. striatus
      |  |-- †D. carinatus Gross, 1973
      |  |-- †D. kleesmentae Valiukevičius, 1986
      |  |-- †D. gravis Valiukevičius, 1988
      |  |-- †D. poltnigi Valiukevičius, 2003
      |  `-- †D. solidus Valiukevičius, 2003
      |--o †Gladiobranchus Bernacsek & Dineley, 1977; L. Dev. NNA.
      |  `-- †G. probaton
      |--o †Ptychodictyon Gross, 1973; L.Dev. WNAm., M.Dev. EEu. 
      |  |-- †P. rimosum Gross, 1973
      |  |-- †P. sulcatum Gross, 1973
      |  |-- †P. distinctum Valiukevičius, 1979
      |  |-- †P. ancestralis Valiukevičius, in Valiukevičius & Karatajute-Talimaa, 1986
      |  `-- †P. americanum Burrow, 2007
      `--o †Rhadinacanthus Traquair, 1888
         `-- †R. longispinatus

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