In H. G. Wells's The Time Machine, the subterranean species living below the surface is the Morlocks.
The Morlocks inhabit the underground world of A.D. 802,701, maintaining ancient machinery beneath the future English countryside. Their pale, light-sensitive appearance reflects their long separation from the surface, while their underground society has retained practical skills and technological knowledge that the surface dwellers have lost.
The Time Traveller initially believes that the gentle Eloi are the only descendants of humanity. He later discovers that the Morlocks operate the wells and tunnels connecting the underworld to the surface. The story suggests that the two species evolved from Victorian class divisions: the Eloi descend from the privileged upper class, while the Morlocks descend from the laboring class.
A major twist is that the Morlocks no longer serve the Eloi. Instead, they provide for them and eventually hunt them as food. Martians and Selenites belong to other fictional worlds, while the Eloi are the separate surface-dwelling species in Wells's novella.