Utahnax's preserved section is roughly 6 cm (2.4 in) long, with at least eight pairs of ventral flaps similar to those found on Kerygmachela.

Its lack of lobopods also suggests it was primarily if not wholly pelagic, occupying a similar niche to radiodonts.

This may explain the paucity of gilled lobopodians in the fossil record, as they may have competed with radiodonts in the pelagic predatory niches.

[2] The genus name Utahnax is derived from Utah, where it was found, and the Greek word anax, meaning “king” or “ruler”.

The species name vannieri honours Jean Vannier for their extensive work on fossil ecdysozoans.