As of 2018,[2] 7 monotypic genera of cheloniellids had been formally described, whose fossils are found in marine strata ranging from Ordovician to Devonian in age.

Cheloniellida has a controversial phylogenetic position, with previous studies associated it as either a member or relative of various fossil and extant arthropod taxa.

[1][2] Cheloniellida has a controversial phylogenetic position within arthropod higher classifications, with studies mainly around 20th century suggested it as a relative/member of either Crustacea, Trilobita, Chelicerata or Aglaspidida.

[23][3][24][25][4] The clade was formally named Vicissicaudata in 2013,[3] united by a differentiated terminal trunk area (postabdomen) that bears a pair of non-leg-like appendages.

[3][4] Numerous phylogenetic analyses also retrieved Vicissicaudata within Artiopoda,[4] a diverse arthropod taxon comprising trilobites and similar fossil taxa that may[26][24] or may not[3][25][4] be closely related to chelicerates.