Mole-man

The Mole-men are a sapient species of subterranean creatures which live in deep underground cave systems on the planet Mercury.

Biology
The Mole-men are vertebrates which stand about 4 ft in height (~ 1.2 m), with an ovoid head attached to an oblong body covered in reddish-brown hair. Their arms are short and their legs are practically nonexistent. Instead, they have long mobile feet equipped with a large number of powerful suction cups, which allow them to cling to rock surfaces easily.

Being accustomed to Mercury's scorching temperature, heat-rays have no effect on the Mole-men. At night, they retreat into their subterranean cave systems, kept warm by volcanic heat, as they can't withstand the cold night of the surface. Although they live in the proximity of volcanoes, they can't survive inside the actual volcano, as the gases are fatal to them.

Appearances

 * "The Mole-Men of Mercury", by Arthur K. Barnes (1933)