There are at least 4 reproductive patterns in tubeworms: 1) brooding outside of tube, 2) brooding inside of tube, 3) broadcasting gametes, and 4) exhibiting poecilogony. 

Sabella media is a small hermaphroditic sabellid worm that lives in soft membranous tubes often found sandwiched between compound ascidians and rock, or among the holdfast haptera of brown alga Hedophyllum sessile.  Studies in San Juan Island and Friday Harbor Laboratories, Washington show that its mode of reproduction is to brood eggs outside the tube. The eggs, about 1000 at a time, are placed in doughnut-shaped cocoons attached to the outside of the tube aperture.  Development takes place within the cocoon and the eggs hatch to a swimming metatrochophore larva, with 3-segments or setigers, after about 8d at 12^oC. In laboratory culture, the larva swims demersally for a day, and metamorphosis occurs gradually over a period of about a week.  By 21d of age the juvenile has 6 segments and, by 30d, 8 segments with 4 pairs of gills.  The authors note that Sabella’s life history combines the protective benefits of brood protection with some dispersal during a short swimming stage.  McEuen et al. 1983 Mar Biol 76: 301.

NOTE  adults are 15mm in length and possess about 45 segments

NOTE  at the sea bottom