Calkinsia is a monotypic genus of alga comprising the single species Calkinsia aureus. It lives in low-oxygen seafloor environments. It is not classified in any of the three well-known groups of the Euglenozoa (Kinetoplastida, Euglenida or Diplonemida), but is placed in its own group, the Symbiontida (along with some DNA sequences which were found in marine environments but not identified with known organisms). Some authors have classified Calkinsia alongside Postgaardi, but Postgaardi has not been studied well enough to test this hypothesis.