Folks tend to forget that sponges are indeed animals. Sponges, like other animals, are made up of many cells and cell types (multicellular), produce sperm cells and they are heterotrophic (this means an organism that cannot make its own food). Sponges differ from other animals in that they do not form true tissues or organs.
So, how do they do it? Researchers are not really sure because there's not much research in the first place. Scientists from the University of Barcelona believe that a sessile and stable lifestyle favors long life. Humans are rapidly threatening all species and rising water temperatures, pollution, and habitat disturbances may threaten to eliminate uncovering how some sponges can live an amazingly long time.