Credit: Credit: Charles E. Mitchell
A microscope image of a colony of Styracograptus tubuliferus, an ancient, deep-water graptolite that belonged to a lineage of graptolites that later disappeared during the end-Ordovician mass extinction. Each colony consists of a chain of tubes that make up a communal edifice, and each tube housed an individual graptolite animal. Credit: Charles E. Mitchell