This character is a member of Selar's family.

Xyon (known simply as "Xy") was a half-Vulcan, half-Hermat hybrid born to USS Excalibur officers Burgoyne 172 and Selar in the year 2376. He was named in honor of Xyon of Calhoun, the son of Mackenzie Calhoun who was at the time of Xy's birth believed to be dead.

Xyon's unique hybrid nature caused him to age and mature rapidly. His mother, Selar, spent most of her off-duty hours trying to find a way to reverse Xyon's rapid aging.

By 2379, the barely three-year old Xyon was fully mature and educated, and even served as science officer onboard the Excalibur. (NF novels: Dark Allies, After the Fall, Missing in Action)

In 2380, the regenerative metabolism of an injured Hermat named Rulan 12 provided the key to slowing Xy's rapid aging, allowing him to live for approximately 100 years. Unfortunately, during the course of the mission that led to this discovery, Selar was killed. (NF novel: Treason)

After the death of his mother he temporarily took over her duties as CMO.(NF novel: Blind Man's Bluff)

USS Excalibur personnel
USS Excalibur (2240s)	R. Bannock
USS Excalibur (NCC-1664)	T. Haleakala-LoBrutto • A. Harris • J.T. Kirk • H. Ogden • Thonen • M. Walsh
USS Excalibur II	Preye
USS Excalibur (NCC-26517)	Argyle • R. Beth • Boyajian • Burgoyne 172 • M. Calhoun • M. Christiano • Howard • M. Gold • Hecht • M. Houle • Janos • Z. Kebron • M. Korsmo • Kothari • K. Kurdziel • G. La Forge • R. Lefler • Lowe • Martins • Maxwell • M. McHenry • Meyer • C. Mitchell • Morgen • W. Morrison • K. Mueller • Ramirez • W.T. Riker • B.G. Robinson • Scannell • Selar • Shastakovich • E.P. Shelby • Soleta • Somak • R. Takahashi • Torelli • T'Shanik • D. Voyskunsky • P. Watson • M. Wilkarah • Yates
USS Excalibur (NCC-26517-A)	Burgoyne 172 • M. Calhoun • Candido • Dreyfuss • Janos • Z. Kebron • R. Lefler • M. McHenry • Selar • E.P. Shelby • Soleta • T. Tobias • Xy