Haplosclerids are distributed worldwide, even in freshwater. They stand out as sponges that can tolerate an unstable home environment. You find them in places like estuaries that suffer regular changes in salinity and water levels, tropical marshes that dry up in summer, and high elevation lakes that freeze in winter. How can a sponge survive these fluctuating environments Haploscerids usually alternate between sexual and asexual reproduction, and can go asexual when conditions are bad. They produce buds made of cells and a food supply called gemmules, which are little miracle packets that can survive freezing and drying. If it gets too dry, gemmules go into a torpid state called estivation and, if it gets too cold, they hibernate. The adult sponge may die, but leave behind a bunch of gemmules that can wait and begin to grow again when conditions improve.

Sponges have an internal skeleton, but it is not made of bone like ours. Their skeletons are made of stiff, mineral rods called spicules, or a matrix of strong but flexible protein called spongin, or both. Spicules may be loosely scattered in the body tissue of a sponge, gathered into little bundles, or arranged in symmetrical patterns to form a structured skeleton. You can judge a sponge by its spicules. They come in many shapes, from as simple as toothpick-straight to complex, branching stars. The end of each spicule is specialized too; it may be pointed, flat, shovel-like, or even look like a mushroom cap. By using microscopes to look at spicules (which are tiny), scientists are often able to identify the type of sponge they came from. Given that the spicules are often all that remain of a dead sponge, this is quite handy.