It may come as a surprise to learn that sponges are actually made from marine life. However, there are different types of sponges. Most household sponges are man-made from cellulose or plastics. But these natural sponges are actually made from the endoskeleton of a marine animal.
Sponges are a primitive and peculiar group of animals. They are so different from other animals that they were once classified as a separate sub-kingdom called the Parazoa, meaning "almost animals." They have no organs, no nervous system, digestive system, body tissue, or reproductive organs. Their bodies are basically a collection of cells in a jelly-like matrix, supported by a framework of proteins and calcium carbonate..
But my favorite thing about sponges is their ability to re-aggregate. If you take a live sponge and press it through a fine mesh, it will break down into a slurry of individual cells. But since the cells are really good at recognizing each other they can actually come back together and re-form a whole sponge.
You can even make a "mixed sponge smoothie", blending together cells of different species. But you can't fool a sponge! The cells from each individual sponge will only reconnect with each other and not mix with cells of the other species or even with cells from different individuals of the same species. So eventually your smoothie will re-aggregate into whole sponges just like you had before.