Other contributors of mass to the reef include stromatoporoid sponges, some forming bumpy mounds, others short and grasslike. Some forms had sieve-like colonies, which allowed water currents to flow through. These microscopic animals fed on plankton. Perhaps because they shared an ecological niche similar to corals, bryozoans were not abundant while the coral patch reef was living. Trilobites were mobile scavengers, crawling around the sea bottom, much like lobsters today.
Trilobites shed their skin as they grew by molting.
Most fossil finds are of these molts. Three species are depicted in the center section of the diorama. Brachiopods are not clams, their internal anatomy and shell symmetry is different. These were stationary creatures, like barnacles are today. The shelly animals were much more abundant after the coral patch reef had been buried by sediment.