Sedentaria

Sedentaria
Examples of Sedentaria (clockwise from upper left corner): Sabellida, Echiura, Maldanomorpha, Clitellata, Terebelliformia, Siboglinidae.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Annelida
Clade:	Pleistoannelida
Clade:	Sedentaria Lamarck 1818
Orders and families
Orbiniida Cirratuliformia Siboglinidae (=Pogonophora) Sabellida Spionida Opheliida Capitellida Echiura Capitellidae Terebelliformia Maldanomorpha Clitellata "Oligochaetes" Hirudinea Incertae sedis ?Myzostomida ?Spintheridae

Sedentaria is a diverse clade of annelid worms. It is traditionally treated as a subclass of the paraphyletic class Polychaeta, but it is also a monophyletic group uniting several polychaetes and the monophyletic class Clitellata. It is the sister group of Errantia.^[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 .^[2]