this paper from 2008 describes a Eukaryote that has lost its mitochondria - as I briefly mentioned in class. In this case though the remnant mitochondria, known as a mitosome, actually consumes ATP - that the host cell must absorb from its host. Reversing the usual relationship between mitochondria/mitosome and host cell. Funky.
Thus, uniquely among eukaryotes, the traditional relationship between mitochondrion and host has been subverted in E. cuniculi,
by reductive evolution and analogous gene replacement. Instead of the
mitosome providing the parasite cytosol with ATP, the parasite cytosol
now seems to provide ATP for the organelle.