Sea Emperor Leviathan

The sea emperor is a passive filter feeding leviathan native to the planet 4546B. It is a highly endangered species. The sea emperor secretes a substance that kills the Kharaa bacterium called "Enzyme 42" and is what cures the player at the end. The allegedly last member of this species was trapped by the precursors so she makes more sea emperors so they can cure the multi planetary bacterium. However, the sea emperor eggs need an enzyme to hatch. The sea emperor was unable to telepathically speak with the precursors and couldn't stop them from trying to prematurely hatch an egg, killing the embryo in the process. The player is given the blueprint of the enzyme so the eggs can hatch and cure the planet.