Tunicates are a group of marine filter-feeding animals that have been traditionally divided into three classes: (1) Appendicularia, also known as larvaceans because their free-swimming and pelagic adult stage resembles a larva; (2) Thaliacea, which includes three orders of free-swimming and pelagic adult forms with complex life cycles (Salpida, Pyrosomida, and Doliolida); and (3) Ascidiacea, colloquially referred to as sea squirts, which is comprised of diverse sessile solitary and colonial species and includes some of the most extensively studied tunicates. It was mainly the ascidians that served as the inspiration for seminal studies in developmental biology and evolution conducted last century by British zoologist and prolific writer N. J. Berrill, whose quote appears above