The species possess long cylindrical bodies with sclerites (skeletal plates consisting of ventral sternites, lateral pleurites, and dorsal tergites) fused into complete rings.

Juliformians also lack Tömösváry organs and have a large collum (first body segment) which overhangs the rear of the head.

[4] The Xyloiuloidea is an extinct superfamily of fossil millipedes of uncertain placement within the Juliformia.

Known from the Lower Devonian to the Upper Pennsylvanian, Xyloiuloidea consists of four families and several genera.

The group was formerly considered a suborder of Spirobolida, but newly discovered species in 2006 required a reconsideration of classification, and the order to which Xyloiuloidea belongs remains undetermined.