They can reach up to in length and are pale gray, with red tentacle-like gills on their heads. Perhaps most fascinating, their tail ends are often resting in temperatures as high as , while their feather-like heads stick out of the tubes into water that is a much cooler, . Scientists are attempting to understand how Pompeii worms can withstand such extreme temperatures by studying the bacteria that form a "fleece-like" covering on their backs. Living in a symbiotic relationship, the worms secrete mucus from tiny glands on their backs to feed the bacteria, and in return, they are protected by some degree of insulation. The bacteria have also been discovered to be chemolithotrophic, contributing to the ecology of the vent community. Recent research suggests the bacteria might play an important role in the feeding of the worms.