Mine just came in on my rock. We have red ones, white, brown, striped, and some that seem to have 2 fans coming out of 1 tube. They are all pretty small and dont'seem to propagate easily, although we do have a large colony of white billowy ones - they sometimes "spawn" together. Haven't noticed 'babies' but I've only had that rock a couple months.
HEre's a pic of the bottom of the colony. some of the worms have gone into their tubes due to the forraging antics of Moto, my scooter blenny.