Non-Placental Species Xiphophorus hellerii (image) University of California - Riverside Caption This is non-placental species Xiphophorus hellerii. Note the beautiful ventral extension of the tail fin. Credit Juan Carlos Merino. Usage Restrictions None 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.