ALGAE are a type of simple plant life and are found in a wide variety of modern environments. Those living in the sea are commonly known as "seaweeds." The many small, green to yellow-green, bushy objects placed throughout the Silurian reef diorama are meant to represent algae as reef dwellers. This reconstruction is highly interpretive. Fossil seaweeds like those pictured here are known from a few Silurian deposits, but only one has been found in Silurian rock in Wisconsin or Illinois. Nevertheless, algae and microbial organisms that secrete calcium carbonate were present as binders in the Silurian reefs, as indicated by layered, crust-like growths around other fossils.
RECEPTACULITIDS are an extinct group of organisms whose biologic affinities are unknown. Some paleontologists have interpreted them as a type of algae (that is, a sea-dwelling plant), and other paleontologists have considered them to represent a sponge-like animal. The receptaculitid skeleton is made of spiral rows of small attached plates. Receptaculitids were a minor group of dwellers in the Silurian reefs of Wisconsin. Two species have been reconstructed in the diorama.