Latticework -- Part 2

Okay, here we go — the answer to last night's mystery.

This story started during a beach walk on 12 January 2017.  And I'll admit, it has to do with something that drives me crazy — walking by an animal on the beach that I can't identify.  Especially when it seems like it should be identifiable, e.g., when you see the same obvious and distinctive structures over and over again.

For example, we kept encountering these clear blobs on the beach. Each of them was about the same size, and each had a noticeable purple teardrop-shaped globule.  Here are two examples:

 

 

See what I mean?  It had to be something.  It appeared to be part of an animal of some kind.  It wasn't just a random bit of goo on the sand.

I was a little frustrated that I couldn't tell what it was, but I kept looking and hoping that we would fine one with more "parts" that would reveal the identity of the animal.

And then Eric decided to place one of the blobs in some water.  They were incredibly thin and fragile and difficult to pick up, but this step was critical.  Here are two pictures of the blobs when floating:

 

 

These specimens were tattered after having come through the surf, but I hope you can see that we now had more clues.  In water the blob expanded into defined structures — broad wings, with a latticework-like design!

This brought to mind an illustration which you might recall from a post in 2012:

 

Modified from The Light & Smith Manual: Intertidal Invertebrates from Central California to Oregon (2007) 

 

Yes, this is the pteropod Corolla spectabilis.  And the blobs observed during our beach walk on 12 January 2017 represented my first close look at Corolla's wings.  I know many of you have been finding Corolla pseudoconchs on the beach this winter.  The wings are easily separated from the pseudoconch, and they're probably torn apart in rough seas, so they're not often seen on the beach.  

[In the illustration above, also note the "viscera."  The purple globule attached to the wings is a part of the gut (included in the viscera).]

For some reason, quite a few Corolla wings were washed up on 12 January, so it was a rare opportunity to observe them and the muscles in the wings.  [Remember that Corolla and other pteropods are sometimes called "sea butterflies."]

Here's the close-up again from last night's post, showing the fascinating muscle bands running through the wings:

 

Having seen these specimens and the pattern of the muscle bands under the microscope, can you tell what's missing from the illustration shown above?  Although there are muscle bands drawn in two directions, there's a third set at a different angle.  For the drawing to be accurate, you'd need to add one more set of muscle bands.  The latticework of muscles may be important in achieving the upstroke and downstroke of the large wings as the pteropod swims through the water.

Mystery solved!  And now if we see these blobs washed up on the beach again, we'll know what they are.

P.S.  Click here to watch a video of Corolla wings in action.

P.P.S.  And here's a reminder about the more commonly encountered Corolla pseudoconch: