Very little is known about the Kurasians. Their name, even, is conjectural and applied by Admiral Arelim Seron of the Kuras Tetrarchy when he met a living one (brought to life by scientists working for crime lord Breggar Lark). Seron, in fact, was among the few alive who had any interaction at all with the Kurasians, as they had a very short life-span after being revived (probably due to the comparably lower temperatures at that depth). Lark, however, was less concerned with their lives and more so with their deaths.
The Kurasians had been a powerful and thriving society, living in peace and harmony for many years - until the advent of weaponry. No sooner had a Kurasian first discovered a means to hurt another, hundreds, even thousands of new weapons were developed in a matter of decades. Their underground cities were destroyed, and their people were slaughtered. A few tried to escape to the surface, but they, too, were destroyed - along with the flora and fauna of their entire world - when the Kurasian superweapon was used for the first time. Without any geothermal energy to keep them warm, the Kurasians quickly fell to the cold and froze. Their bodies were well-preserved enough to be found by Lark and his scientists, who tried to pull the information on their weapons - biological and chemical weapons, mostly, but also plasmatic and even laser weaponry - for use against the rest of the Galaxy.
The Kurasians that lived briefly then wished that nothing be done to keep them alive; still distraught from the devastation they had caused, they simply wished to rest peacefully. The Tetrarchy allowed them to do so, and then gave them decent burials. The species remains extinct.