Chromalveolates
The supergroup Chromalveolata, a large, extremely diverse clade of protists, has recently been proposed based on two lines of evidence. First, some DNA sequence data suggest that the chromalveolates form a monophyletic group. Some data support the hypothesis that the chromalveolates originated more than a billion years ago, when a common ancestor of the group engulfed a single-celled, photosynthetic red alga. Because red algae are thought to have originated by primary endosymbiosis, such an origin for the chromalveolates is referred to as secondary endosymbiosis.