[2] A fifth class, Concentricycloidea, was proposed for the unusual genus Xyloplax (sea daisies),[4] but was later demoted to the status of infraclass as the sister of Neoasteroidea within the asteroidean sublcass Ambuloasteroidea.

[9] Most authors consider Somasteroidea to be the basal stock from which the other three classes evolved.,[10][11] but an argument in favor of monophyly and a position closer to stenuroids and ophiuroids than to asteroids has also been made.

[13] Somasteroids have been described as being more rigid in shape than derived asterozoans, although this apparent structure could be exaggerated by tissue changes at the time of death.

[14] S Stenuroids were initially seen as early ophiuroids[15] before being promoted to class level, but their evaluation is challenging due to wide variations in morphologies.

[16] A recent examination of Stenuroidea found it to be monophyletic, but allowed that (as with other asterozoan classes), paraphyly or polyphyly could not be entirely ruled out.