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.