1923, Sidneyia, was placed, along with Emeraldella, as part of the group "Xenopoda". Today, both Sidneyia and Emeraldella are placed as part of the clade...
century, Cheloniellida was mostly found to form a clade with Aglaspidida and Xenopoda (e.g. Sidneyia and Emeraldella). The clade was formally named Vicissicaudata...