I believe the answer is decomposition. please let me know if that is correct.
The answer is tunicates. Tunicates are commonly known as sea squirts and are in the Chordata phylum, even though they don't have a back bone. Which is really weird. But they just got put into the same category as humans. This is because they have a notocord and a back bone when they are larvae. But they lose all these when they become adults.
That answer would be A. nucleus
Single circular piece of DNA