Tidepool Tim says,  "These little tubeworms settle, grow, eat, and spawn while living on the fronds of bladderwrack seaweed.  It is rare to find a single worm in any one location - typically they are in large colonies on several fucus plants all in one location. Worms range in size from a mere dot up to the size of an un-popped corn kernel. When the tide flows out these worms seal up their tubes and hopefully don't get too hot or dry out until the tide floods back in.  They have small little tentacles used for feeding which can be seen with a hand lens. They must be broadcast spawners that develop into some sort of planktonic larvae which eventually settle out onto new seaweed plants.  Calcium from the seawater is used to grow a hard, waterproof shell that grows in a clockwise whorl. We collect and sell these as colonies of dozens of tubeworms.”