It was composed of the families Orbiniidae, Paraonidae and Questidae, all of which share in common the lack of antennae and palps, and the presence of an eversible pharynx and biramous parapodia with simple chaetae.

[1] However, through phylogenetic analysis it was found that Questidae and Paraonidae are more closely related to Clitellata and Cirratulida respectively.

[3] Phylogenetic analysis of annelids has found Orbiniida to be the earliest diverging clade of Sedentaria.

At the same time, the other half of "archiannelid" worms, Protodriliformia, was found to be the earliest diverging clade of Errantia.

The convergence between these two groups occurred through progenesis and miniaturization, as a way to adapt to the marine interstitial ecosystem between sand grains (i.e. interstitium).