If you hear about this creature first time, don't worry - you're not alone in that. Our world is pretty rich in different kind of interesting animals. These pretty swimming sea slugs are also sometimes known as cliones, but this is potentially misleading because the family Clionidae is just one of the families within this clade. They are gelatinous, mostly transparent, and very small species reaching 5 cm. Cute cursor pack with fanart blue Sea Angel.