After Kazlev, 2000, and “Wikipedia”, 2012

<==o †Chasmataspidida Caster & Brooks, 1956 [Diploaspidida Simonetta & Delle Cave, 1978]
   |?- †“Eurypterusstoermeri Novojilov, 1959
   |--o †Chasmataspidae Caster & Brooks, 1956
   |  `-- †Chasmataspis laurencii Caster & Brooks, 1956; Ord. NAm.
   `--o †Diploaspididae StÝrmer, 1972 [Heteroaspididae StÝrmer, 1972]
      |-- †Achanarraspis reedi Anderson, Dunlop & Trewin, 2000; Dev. WEu.
      |--o †Diploaspis StÝrmer, 1972 [Heteroaspis StÝrmer, 1972] Dev. CEu.
      |  |-- †D. casteri StÝrmer, 1972 [Heteroaspis novojilovi StÝrmer, 1972]
      |  `-- †D. muelleri Poschmann, Anderson & Dunlop, 2005
      |-- †Forfarella mitchelli Dunlop, Anderson & Braddy, 19994; Dev. WEu.
      |-- †Loganamaraspis dunlopi Tetlie & Braddy, 2004; Dev. WEu.
      `-- †Octoberaspis ushakovi Dunlop, 2002; Dev. NEEu.

Reference(s):