The Moon And Mercury

(See Addendum.)

 In Is There Life On Other Worlds? (New York, 1963), Poul Anderson summarizes data about the Moon:

weak gravity so no atmosphere or water vapor on the surface;
temperature varying from over 200 F to below -250 F;
no protection from Solar ultraviolet or charged particles;
however, large areas insulated by dust have underground temperatures of 30 F to -95 F;
irradiated dust in vacuum congeals into material that could hold organic matter;
low gravity plus probable absence of a core could mean protected caverns and tunnels;
organisms could have originated during the 10 or 100 million years before the Moon lost its air and surface water;
other organic matter could have arrived during the meteoric bombardment, even including Terrestrial organisms;
subsurface ice could become liquid or vapor during the Lunar day;
some organisms could have adapted as the atmosphere was lost and might also use the organic matter left by those that had died.

Scientists speculate at most about microscopic organisms but Anderson imagines:

cactus-like plants;
one symbiont growing a membrane to screen against ultraviolet and retain water;
others using Solar energy to metabolize minerals;
buried nodules manufacturing enzymes to repair radiation damage;
worms or beetles distributing seeds in return for nourishment;
all, when dying, providing matter to the underground ecology.

The Wellsian Moon seems to return if only in Anderson's imaginative projections from current data. He speculates similarly about life in caverns on Mercury, then also hypothesizes very hot liquids as lubricants as in his short story, "Life Cycle", set on Mercury.

Addendum: I try to summarize Poul Anderson's intricate arguments comprehensively and accurately but this time missed a point:

"...because there is no atmosphere and hence no convection, anything that casts a shadow is a barrier to light and radiation. The many Lunar crevasses and caves are never subjected to the Sun's attack." (p. 63)

Thus, in addition to congealed surface dust plus underground caverns and tunnels, all of which I did list, we are to imagine cactus-, worm- and beetle-like organisms in shadows and caves on the surface. (Although I think that the Apollo astronauts would have seen some of them.)