Opabiniids closely resemble radiodonts, but their frontal appendages were basally fused into a proboscis.

Opabiniids also distinguishable from radiodonts by setal blades covering at least part of the body flaps and serrated caudal rami.

[2] Opabiniidae was named by Charles Doolittle Walcott in 1912, alongside its type species Opabinia.

Walcott interpreted Opabiniidae as a family of anostracan crustaceans, most closely related to Thamnocephalidae.

[2] Myoscolex from Emu Bay Shale is sometimes suggested to be an opabiniid,[5] but morphological features supporting this interpretation are controversial.