Suborder Heterostraci is a scientific term used to describe a group of extinct jawless fish that lived during the Silurian and Devonian periods. This suborder is also known by several other synonyms like the heterostracans, heterostraciforms, and heterostracidae. Heterostracans derived their name from the type of bony armor that covered their heads and bodies that were composed of a single layer. They were bottom-dwellers that had unique feeding structures that they used to filter plankton from the water. The classification of these fish has evolved over time and hence their identification and classification are still conversational topics among researchers, but heterostracid is still the official name.