The crab-like Quelni were the dominant species on their planet before the Covenant came. When they refused to join the Covenant because of their conflicting monotheistic beliefs, the Covenant launched an invasion to persuade them. However, when the Arbiter killed their leader, they released their guardian beast: the Lekgolojiri.
They all fought to the death, becoming extinct. However, the Lekgolojiri remembered them and kept up traditions even when the reasons for them died long ago.