Harmonium

Harmoniums are small, apparently semi-sapient organisms indigenous to deep underground cave systems of planet Mercury.

Biology
Semi-transparent blue in color, Harmoniums are paper-thin and have no visible distinct organs. Their bodies are diamond-shaped, about 30 cm across. Having no eyes or other sense organs, they can only perceive the world through touch and rudimentary telepathic abilities.

Harmoniums feed on nearly undetectable vibrations on the planet's surface. These vibrations are called "Mercury's song". Harmoniums reproduce by "flaking off" tiny fragments that later develop into adult beings. They are biologically immortal (i.e. they never age), but so fragile that it doesn't take much to kill them. When a Harmonium dies, its body shrivels up like dried fruit and changes color from blue to orange.

Harmoniums communicate with an extremely limited language that consists of only two messages. The first is "Here I am". The second, which is an automatic response to the first, is "So glad you are".

Appearances

 * The Sirens of Titan, by Kurt Vonnegut (1959)