There are several synonyms for the suborder Osteostraci, which is a group of extinct, jawless fishes that thrived during the Silurian and Devonian periods. The most common synonym for this suborder is "anaspids," which is derived from the Greek words "ana," meaning "up" or "back," and "aspis," meaning "shield." Another synonym for Osteostraci is "psammosteids," which refers to a family of heavily-armored, benthic osteostracans that lived in shallow marine environments. Additionally, some researchers use the term "cyclostomata" to describe Osteostraci, as they belong to the class Cyclostomata, which includes jawless and armored fishes.