Gelrakians were a humanoid species native to the Federation planet Gelrak V. They had green skin and sharp teeth. Like many other humanoids, they had red blood as well.
The Gelrakians based their entire social structure around crystals. They were sworn enemies of the inhabitants of Mavok Prime.
Their level of technology was disparate, as they had ships equipped with phasers and boarding pods, as well as their own environmental suits, but their handheld weaponry was apparently limited to spears and clubs.
For ground transport, they used hoverbikes and presumably cars. In fact, the leader of their people had plans to make a crystal car to use in their death races, which were to replace their trial by combat.
At some point before or during 2380, they joined the United Federation of Planets, and presented the honor crystal to the first contact team.
In 2380, the USS Cerritos arrived to Gelrak V to further the relationship between the Gelrakians and the Federation. (LD: "Temporal Edict")