If there are only two genera remaining, what happened to the other 24?

Context: According to the World Register of Marine Species, there are only two genera in this family. Previously there were about 26, but most of these have been reallocated as sub-genera of the remaining two genera, Mycale and Phlyctaenopora:

Answer: Most of the other 24 were reallocated as sub-genera of the remaining two genera.