very difficult to identify sponges. very little literature, and even less info on the net. to id a sponge, you need a microscope, you won't be able to id them by looking at them. Based on where they originally grown, there shape and color can vary greatly, even within species. Some of the larger and more complex sponges are easily id'ed, but encrusting sponges, and the kind you have there will take an expert in the field, and a microscope. Might as well call it white branching sponge or something like that.