Imagine that some members of an aquatic species of motile, photosynthetic protists evolve to become parasitic to fish. They gain the ability to live in the fish gut, absorbing nutrients as the fish digests food.
Over time, which of the following phenotypic changes would you expect to observe in this population of protists?

A) loss of motility
B) loss of chloroplasts
C) gain of a rigid cell wall
D) gain of meiosis