(spire-owe-stow-mum) is a genus of heterotrich ciliates, and some species in this genus may extend up to 1 mm in length. With a line of membranelles leading from the anterior of the cell to the cytostome which is located about half way down the cell. Contractile. The dark central structure is the macronucleus Contractile vacuole at posterior end of cell. In habitats with low oxygen. Phase contrast.