Incertae sedis Sedentaria is a diverse clade of annelid worms.

[1] Sedentaria are mainly found within marine environments that have low oxygen levels  and are specially adapted to these low oxygen environments by  increasing gill surface area and having high-affinity respiratory proteins.

Furthermore, they go through a process of metabolic depression which lowers their energy use so that they can inhibit these low oxygen zones .

[3] Other groups that are nested within Sedentaria are: Clitellata, the Sabellida/Spionida clade, Opheliida, Echiura, Cirratuliformia, Terebelliformia, Maldanomorpha and the families Siboglinidae and Capitellidae.

[4][1][5] Errantia Orbiniida Cirratuliformia Siboglinidae Sabellida Spionida Opheliida Echiura Capitellidae Terebelliformia Maldanidae Arenicolidae Clitellata 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.