Looking out

Below is a close-up mystery photo for you.  I know it might be challenging, but it's always fun to have a chance to wonder.  Can you guess what structures these are, or what type of organism it is?

 

If you're ready for another clue (or part of the answer), here's a photo showing a larger view:

 

The red mound-like structures in the first photo are compound eyes.  The eyes are located on the radioles (feeding tentacles) of the tube worm, Pseudopotamilla socialis.

July 1st is International Polychaete Day, so it seemed appropriate to highlight these amazing polychaete eyes!  (Polychaetes are segmented worms.)

Here's another view of the radioles of Pseudopotamilla showing the compound eyes:

 

The radioles form a fan or crown just outside of the worm's tube.  The radiolar crown is used for feeding (capturing food particles from the water) and respiration.  Because the compound eyes are found on the radioles, they're called radiolar eyes.

The eyes might serve primarily to detect shadows, so the worm can withdraw quickly into its tube (see below) when a predator (e.g., a fish) passes over.  It's also possible the eyes are involved in more complex visual processing, but further studies are needed.

 

Pseudopotamilla socialis lives in the low intertidal zone along our shores.  It's relatively small, but if you're looking very closely, you might catch a glimpse of its wonderful fan-like radiolar crown.  And if you see the crown pull back in, you'll know that it's possible that the radiolar eyes detected your presence!

Happy International Polychaete Day!

 

P.S.  Many thanks to Leslie Harris for confirming our identification.

 

Banded tentacles

 

A beautiful feather duster worm, Parasabella media, in a rocky shore tidepool.  The tentacles (called radioles) are used to capture suspended food particles from the water and in respiration.  Photographed in northern Sonoma County on 24 February 2017.

Chone

 

A few days ago, I was trying to photograph this beautiful tubeworm under a microscope.  This is Chone sp. (probably Chone minuta), commonly found among surfgrass in the rocky intertidal zone.

When you first encounter them in the field, you might mistake these worms for mats of accumulated shells and sand.  But when you inspect this material closely, you can see that it's made up of many densely packed individual worm tubes that are covered with small shell fragments.  I need a better picture, but this is what they look like at the base of the surfgrass when the tide is out:

 

The worms use their feather-like tentacles for feeding.  While I was looking at them under the microscope, something on the left side of the tentacles caught my eye.  Can you see the horseshoe-shaped piece at about 9 o'clock in the image below?

 

I wasn't sure what it was, so I started searching to see if it showed up in other places (next image).

 

Sure enough, those horseshoe-shape pieces extended between each tentacle.  I didn't know it before that moment, but Chone has webbing between its tentacles!  

Below is a view from the side.  You can see how the transparent webbing forms a membrane below the tips of the tentacles to the opening of the tube.

 

I'm not sure what function this webbing serves, but it has been suggested for another species (Myxicola) with a similar structure that it prevents fine sediment from being drawn up from below and fouling the feeding tentacles.

One more fun and somewhat puzzling observation about Chone.  Sometimes they would pull in their tentacles, leaving only the tips projecting outward at the edge of the tube (see below). 

 

I started calling this the "sun position" because they looked like little suns when they did this. While in this position, the tentacle tips flicked regularly in random sequence.  I don't know what's going on with this behavior, but it was interesting to watch and to wonder about!