Didemnum vexillum is a species of colonial tunicate in the family Didemnidae. The school yearbook is known as "The Vexillum". It is unknown to which military unit the "vexillum" belonged. "D. vexillum" has different forms in different locations. The second censor advances behind the victims, holding a standard ("vexillum"). It was first described from New Zealand as "Didemnum vexillum" by Patricia Kott in 2002. Some "Didemnum" species, including "Didemnum vexillum" and "Didemnum perlucidem" are considered invasive species. The invasive carpet sea squirt, "Didemnum vexillum", was found in the Lough in 2012. It remains unknown what images, if any, were painted or embroidered on the "vexillum". The vexillum is shorter than the wings. Vexillum gorii are about one inch long. The "vexillum", which appears often on Trajan's Column, was not protected but at the top. The "vexillum" was once attached to a piece of reed wood. The bearer of a "vexillum" was known as a "vexillarius" or "vexillifer". Vexillum ovate-oblong, slightly exserted.