Ythiss was a brown-scaled, male Selay who served in the Federation Starfleet in the late 24th century. He was an officer and specialised as an engineer. In the year 2381, Lieutenant Ythiss was a member of the crew of the Luna-class USS Titan. He was part of an away team aboard the type-11 shuttlecraft Holiday to a Sentry refinery orbiting an ice planet. When the Null attacked, the Holiday was destroyed trying to protect a shipment of deuterium bound for the Titan. Ythiss and the away team were transported to the moon-sized FirstGen Zero-Three and eventually made their way back to the Titan. (TTN novel: Synthesis)