Legacy of Aru Kararu

In the 26th century, humans discover a humanoid race living on the distant world GO/7498/2, a dark-skinned, golden-eyed people who seem to eke out a primitive, carefree existence. However, a scout team from Earth discovers that there is more to them than meets the eye--they live in symbiosis with vicious reptilian parasites, and the Terran scientists have upset the delicate natural balance.

(Source: The Anime Encyclopedia)