Argo was an inhabited planet, homeworld of a humanoid species known as the Aquans. Other lifeforms included algae, fish, and the sur-snake. Plant life included sea foliage and plants reminiscent of trees on land. The underwater landscape included at least one reef barrier. Its north polar sea was completely uninhabited. According to The Worlds of the Federation, Argo was the first planet in the UFC 78856 system and the Aquans referred to it as "Hestalor." Argo was classified as an N class planet. According to Star Trek: Star Charts (p. 27), Argo was classified as a O class planet.