There are several types of tube worms, each with their own niche. Some occupy existing holes in the rock, while others actively chew their own hole. Some secrete a sticky substance that they use to build a tube around them, similar to FW caddis fly larvae, while others build a stony tube for themselves. Cool things to check for! The feeding mechanisms vary as well--the feathery type, with their filtering fans, to the 'fisher's--the little guys that spit out a sticky string to catch particles, to ones that sneak out at night and search for food.