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. 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.
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. 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.