Postgaardi mariagerensis is a species of single-celled eukaryote in the Euglenozoa

Euglenozoa

The Euglenozoa are a large group of flagellate protozoa. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. There are two main subgroups, the euglenids and kinetoplastids...

. Some have classified it in a class called Postgaardea along with Calkinsia

Calkinsia

Calkinsia is a genus of alga comprising one species. It lives in low-oxygen seafloor environments. It is not classified in any of the three well-known groups of the Euglenozoa , but is placed in its own group, the Symbiontida...

, but as of 2009, Postgaardi is not well enough known to confidently determine its relationship with other organisms in the Euglenozoa. Both it and Calkinsia do live in low oxygen environments and are covered with bacteria which live on their surface.