Amphioxus Head 15x (image) Marine Biological Laboratory Caption This is the head of the marine invertebrate amphioxus (Branchiostoma floridae), magnified 15 times. Amphioxus are the most ancient of the chordates (animals whose features include a nerve cord), according to molecular analysis. They are important to the study of the origin of vertebrates. Credit Maria del Pilar Gomez/MBL Usage Restrictions Please use with proper credit. Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.