Xiaoshiba Biota of Yunnan, China, and a valid species of Sidneyia from Chengjiang, Sidneyia malongensis.

In 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 Vicissicaudata within Artiopoda, which includes trilobites and other arthropods with similar bodyforms. However, Sidneyia and Emeraldella are usually not recovered as