Carpenter Worms

Slithering through the ruins of collapsed mine, a massive rope of muscle and pulsating, slimy skin feasts on the long rotted leftovers of a very unlucky grick. Suddenly, the sound of stone grinding on stone echoes throughout the cavern and the creature darts with surprising speed away from the light that has begun to pour in through the rear of the tunnel. Five plucky adventurers enter the room, intent on reaping the spoils of the underdark; they will never leave this room. The final thing the elven ranger of the group sees, is a tidal wave of muscles, slime, and ancient mining tools held in place by slime that may as well be concrete.
Carpenter worms range in size from less than a foot to over 20 feet. They are pale grayish worms covered in a thick pus-yellow slime that reeks of mildew. While it has a simple toothless mouth the creatures lack eyes, noses, or external sensory organs, instead relying entirely on their permeable skin and light sensitive patches to seek out prey and hide from sunlight. Carpenter worms use their senses to search for rotting matter and curl up in it to dissolve the rotting flesh or plants with their slime before reabsorbing it into their bodies. They react aggressively to any creature it perceives as having invaded it's territory, which consists of the 100~ feet around their brood pouch and about 10 feet around their current food source. 
The Carpenter worm has a unique form of defense wherein it will cover its body in the hardest materials in the immediate area and attempt to constrict or batter enemies to death, it does this by allowing the object to permeate through its slime until it touches the worm and then dehydrating it's slime to the point that it becomes as hard as rock and thus fusing it to the worm, the slime can then be rehydrated by pushing water through it's skin, this process can be done with unerring accuracy so that the worm loses as little moisture as possible. This slime is vulnerable to dehydration and must be kept moist, thus consigning carpenter worms to specific above-ground biomes where they can stave off dessication, but affords them a large territory underground where they can roam in search of detritus.
They have a symbiotic relationship with flail snails where the snail provides them with material to make their armor out of, namely glass and bits of shell; while the worm provides protection to the snail and will often chase off creatures that compete with the snail for food. The snails will initiate this parternship by swallowing the eggs of a carpenter worm and allowing them to gestate within the snail's stomach, this causes the worm to view the snail as the center of it's territory.