Beautiful, beautiful worms. Need to look them up. Fairly sure I've seen (and possible photographed) these before. Time to learn them...

Update: after consulting Light's, Kozloff, BPT, and this dead ringer of a photo at CalPhotos I think this is probably Phragmatopoma californica, the common sandcastle worm. Can anyone confirm? Each tube was no more than 1-3 cm long. Observed in a kelp holdfast at ~30 ft depth, off Pacific Grove, CA.

Also of note: an NYTimes article on researchers studying this worms sand adhesive for biomedical applications (or perhaps "biomedical inspiration" would be more accurate). Via oceanwire.