Agnatha was an aquatic lifeform native of the planet Jezero. A career diplomat, Agnatha was Jezero's ambassador to the Federation in the 23rd century. As an aquatic lifeform with a long, eel-like, tentacled body, Agnatha required a life support tank at all times while aboard Federation starships and starbases. Agnatha was able to communicate with those outside of his tank by the use of a specialized, built-in, universal translator unit.