Chthonians (/ˈθoʊniənz/ from Greek: chthon, "earth") are worm-like creatures in the Cthulhu Mythos. Chthonian, as a name for the species, is the creation of English horror writer Brian Lumley and was first featured in his short story "Cement Surroundings" (1969)—though the creature never made a direct appearance. The Chthonians had a more prominent role in Lumley's novel The Burrowers Beneath (1974), whose title is taken from one of the stories said to have been written by Robert Blake in Lovecraft's "The Haunter of the Dark."
Flowing tentacles and pulpy gray-black, elongated sack of a body...no distinguishing features at all other than the reaching, groping tentacles. Or was there—yes—a lump in the upper body of the thing...a container of sorts for the brain, basal ganglia, or whichever diseased organ governed this horror's loathsome life!
—Brian Lumley, The Burrowers Beneath
Chthonians are described as having heads resembling immense cephalopods, with elongated worm-like bodies coated with slime. Despite their squid-like appearance, chthonians are actually land-dwellers and are even harmed by water. Chthonians are powerful burrowers which can live for more than a thousand years, and are protective of their young. It is said that a chanting sound accompanies every chthonian, and that by such they can be detected while underground and unseen.
The most important individual chthonian is the gigantic Shudde M'ell, which is worshiped by the rest and is the largest and most malignant of this dread race. It is featured prominently in the aforementioned novel.Lin Carter
Linwood Vrooman Carter (June 9, 1930 – February 7, 1988) was an American author of science fiction and fantasy, as well as an editor, poet and critic. He usually wrote as Lin Carter; known pseudonyms include H. P. Lowcraft (for an H. P. Lovecraft parody) and Grail Undwin. He is best known for his work in the 1970s as editor of the Ballantine Adult Fantasy series, which introduced readers to many overlooked classics of the fantasy genre.