Answer:
The amount of time that the 2 species have been evolving apart.
Step-by-step explanation:
A molecular clock is a figurative term that refers to a technique that uses the mutation rate of biomolecules in order to deduce the time when two different but related life forms started to diverge. In this case, we know that the new organism is related to clownfish, and we would like to know when the two species began to evolve apart.