What is "errantia"

Errantia \Er*ran"ti*a\, n. pl. [NL., fr. L. errare to wander. See Err.] (Zo["o]l.) A group of ch[ae]topod annelids, including those that are not confined to tubes. See Ch[ae]topoda. [Written also Errantes.]

Errantia, occasionally Aciculata, is a subclass of polychaete worms. These worms are found worldwide in marine environments and brackish water.