Little is known about the origins of the Derfi'gassak and the IISS have yet to determine if they are natives of Orkney(Reavers' Deep 2919). The world was first surveyed in 110 however the presence of the Derfi'gassak was not discovered until the next IISS survey ship orbited the planet in 180.
The fluorine-breathing Inheritors inhabit a Dyson sphere created by the Ancients, at Sphere (Nooq 3201). Their whole society relies on technology they do not understand. They are detailed in the books GURPS Traveller: Alien Races 3
The Ithklur, native to Tryylin (Extolian 2514), are the most feared warriors known to man. To an Ithklur, Vargr plunder is a walk in the park; Aslan warrior spirit is the babbling of a toothless child. Other races make such a fuss over violence - why not just do it and enjoy it? To the Hivers, the Ithklur are their trained, elite shock troops, lovingly perfected by millennia of manipulation and social engineering. No finer tool has ever been fashioned. But as far as the Ithklur are concerned, they have the Hivers just where they want them. Who wants to be a boring taxi driver anyway? If the Hivers want to pretend they're in charge, what does it really hurt, so long as they leave the Ithklur alone? Who is manipulating whom? The Ithklur are detailed in the books GURPS Traveller: Alien Races 3 and Traveller the New Era - Aliens of the Rim
Llellewyloly are a radially symmetric species native to Junidy (Spinward Marches 3202), colloquially referred to as Dandelions due to a supposed similarity to that Terran plant. They play a part in The Traveller Adventure.
The Mahkahraik, which means “People of This World” in their native tongue, are a species of warmblooded, bipedal reptiloids native to Ma (Ley 3021). Full details of this race are available as a free download from QLI/RPGREALMS PUBLISHING
The Schalli are an uplifted (genetically-engineered) Dolphin-like piscinoid-like species of air-breathing mammaloids and a natural ally of Humaniti, their creators. Schalli are natural navigators (with a superior sense of 3D and 4D environments), but lack manipulator limbs, a serious handicap for a sophont species. To overcome this handicap, a variety of exoskeleton suits with mechanical manipulators have been created to allow the Schalli to operate in terrestrial environments.
Vegans are an alien species originating on Muan Gwi (Solomani Rim 1717) and inhabiting the Vegan Autonomous District. They are named by humans after the bright star near their homeworld. They are of some importance in the Third Imperium when they were granted them a small semi-autonomous state as a counterbalance to the racist Solomani Confederation.