Sammancerxia symbiotae
A symbiotic cooperative between Protosammea Massa and Protomancerxia Megaflagella. The smaller massa was able to attach itself to the surface of megaflagellis. massa benefitted from the mobility of megaflagella, allowing it to escape predators and reach sunny spots, while megaflagella was rewarded with large amounts of glucose produced by the superior photosynthetic abilities of massa.
An freak accident during mitosis at one point resulted in the grafting of the massa genome into that of megaflagellis, meaning they are now truly one species. Reproduction is by binary fission, although the success of this is beginning to fall due to the relative complexity of the organism and many die during the process.
Megaflagellis also lost the use for its proboscis and it soon disappeared.