STROMATOPOROIDS are an extinct group of sponges that formed a hard compact skeleton. Stromatoporoids lived only in seawater, and like modern sponges, they created currents to pump water in and out of their body, where they filtered out tiny food particles. The stromatoporoid skeleton, which was often quite large, generally had a dome-like form (figures 1, 2).
Stromatoporoids were a major type of reef constructor. Two species are shown in the diorama, but stromatoporoids have received little scientific study in the Silurian reefs of Wisconsin and Illinois, and their actual number of species is unknown. An additional type of smaller sponge, which functioned as a reef dweller, is also present in the diorama (figures 3a, 3b).