Cryptic sponges are highly desirable filter feeds that can help a ton with nutrient export. Many reefers today are trying to incorporate them more into their tanks for that reason. Some are also using clams or tunicates for the same reason. i think sponges make their structure with silica (or some do anyway) if you tank is still relatively new you might just be having a bit of a bloom because of excess silica on the glass and equipment rock etc. I would try to leave any that you can that aren't immediately threatening your stock. They will most likely find a balancewhen you tank stabilizes more and you won't have nearly as many. You may have or still may notice similar population explosion with those little stars or feather dusters or other things that suddenly appear and then achieve alarming numbers. Granted you probably don't want to lose zoas to the sponge, but scrubbing them off in the tank is more likely to spread them even more than simply waiting to see what they do. Most of my sponges stay well clear of the lighted areas (cryptic meaning mysterious and in the dark) and have grown right up next to zoas, but have never bothered them. Top Water's evil sponge is a first for me though so if someone has info on that species, I should probably know about that based on my lack of alarm here.
The other critters are probably copepods or amphipods, but the best part about SW vs. FW tanks is that you just never know what you are going to get. I love flashlight and magnifying glass time with the tank at night.