Extratubular

 

While tidepooling today on Bodega Head, Eric called me over to look at something unusual.  Can you see the small greenish-colored animal near the center of the photo above?  (It was ~5 mm across.)  In the field we thought it might be a sea anemone, but it looked odd and if it was an anemone, we weren't familiar with the species.  We decided to bring it back for a closer look.

Here's what it looked like under a microscope:

 

Surprising!  Now we could see that the tentacles were very long and feathery (with side branches).  And what looked like the column or body of anemone in the field was actually a round donut-shaped gelatinous mass containing lots of white embryos!

The structure of the tentacles made it clear that this was a feather-duster worm.  But the egg mass was puzzling.  Neither of us had seen a worm that brooded its embryos like this.  

Here's a close-up of the beautiful tentacles, called radioles.  (The side branches are called pinnules.)  The tentacles are used to capture food from the water and in respiration.

 

And here's a view of the white embryos embedded in the clear, gelatinous ring.

 

We started searching the Internet for a possible identity and it turns out that this type of brooding is rare in feather-duster worms.  We very quickly narrowed the choices.  And after reviewing basic characters, habitat, and life history, we think this might be Parasabella media (formerly called Sabella media and Demonax medius).

Remarkably, this species attaches an extratubular ("outside-of-the-tube") egg mass to the outer lip of the tube it lives in.  [Most sabellid worms either broadcast spawn or brood within the tube.]  The worm protects and cleans the egg mass with its arching tentacular crown.  

The worm can withdraw into its tube.  We were fortunate to capture this on film.  The first photo below shows most of the worm pulled in, with just the tips of the tentacles showing in the center.  The following photo shows the worm deep within the center of the egg mass.

 

 

We don't know if this species has been documented on Bodega Head yet.  We're looking into one possible record, but it might be a first!

In a paper about sabellid worms in the northeast Pacific, Banse (1979) describes this species:

"...specimens were found with eggs deposited in a ring of jelly around the opening of the tube; the opening was flush with the surrounding encrusting organism. With the tentacular crown spread-out, the animals appeared to the naked eye as small Anthozoa." [Anthozoa includes anemones and corals.]

It seems we weren't the first to puzzle over whether this extratubular brooding worm might be an anemone!