If there are only two genera remaining, what happened to the other 24?
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:
user
Most of the other 24 were reallocated as sub-genera of the remaining two genera.
assistant