Biologists figured out that chloroplasts were descended from free-living cyanobacteria about 50 years ago, and lots of evidence has been accumulated since then, but many people have trouble understanding how this could occur even after it has been clearly demonstrated that it did occur. Well, at the unicellular level lots of similar interactions are still happening, and here's a newly described species that still operates by keeping its options open by generating a hetertrophic offspring and a photosynthetic autotroph, via a symbiosis, with each cell cycle. One daughter cell keeps the photosynthetic symbiont, the other by necessity returns to a heterotrophic life style, until it happens upon the right photosynthetic prey allowing it to switch back. This will be a great new example of what an intermediate stage in the evolution of chloroplasts was thought to be. HT to Lab Rat.