Molteye

It hauls itself across the black-glass fields on stubby limbs, the great eye swiveling to track anything warm, and it feeds by fixing that gaze on prey until the heat alone drives it out of cover. The crust that armors it is genuinely rock, shed and reformed as the creature grows, so a Molteye's old shells litter its range like discarded pottery. It sleeps with the eye lidded to a dull ember, and the temperature of a whole cave drops noticeably when it does, the surest sign to a shivering researcher that the local Molteye has, at last, gone to sleep.