Bell in a sense that excluded Holothuroidea, Eleutherozoa was expanded by F. A. Bather in his 1900 taxonomy to include all free-living echinoderms.

Bather considered the taxa within Eleutherozoa to have descended from the other subphylum in his two-subphylum system, the Pelmatozoa, either from different subgroups or at "widely different periods.

[4] With the advent of cladistics, the taxonomy of echinoderms was re-evaluated, finding new support for both Pelmatozoa (in its original sense, per Leuckart, encompassing only stalked forms) and Eleutherozoa, with Echinozoa now having its modern contents of Echinoidea as the sister to a clade containing Holothuroidea and the extinct (and possibly paraphyletic) Ophiocistioidea.

This clade, as sister to the Asteroidea, was given the name Cryptosyringida, constructed from the Greek "kryptos" (hidden) and "syringos" (pipe or fistula), referring to the hiding of certain anatomical elements during development.

[10] More recent work has shown, through multiple lines of evidence, that Asterozoa, consisting of the classes Asteroidea and Ophiuroidea, is the sister group of Echinozoa within Eleutherozoa, disproving the Cryptosyringida hypothesis.