Errantia is a diverse group of marine polychaete worms in the phylum Annelida.

Traditionally a subclass of the paraphyletic class Polychaeta,[4] it is currently regarded as a monophyletic group within the larger Pleistoannelida, composed of Errantia and Sedentaria.

[5] Two groups are nested within Errantia: Aciculata (Eunicida + Phyllodocida) and Protodriliformia (small meiofaunal worms such as the Protodrilida).

[3] Amphinomida Lobatocerebrum Sipunculida Eunicida Phyllodocida Protodrilida Polygordiidae Sedentaria Some taxa, such as Spintheridae and Myzostomida, are still difficult to place due to their long branching, but they likely belong to either Errantia or Sedentaria.

In 1977 the zoologist Kristian Fauchald split Errantia into three orders: Phyllodocida, Amphinomida and Eunicida, giving way to this classification.