Angel on the sand

Returning from a bird survey on Salmon Creek Beach, I was walking along the lower part of the beach near the surf.  I'm always interested in gelatinous animals washed ashore, so I was watching for anything noteworthy.  I was seeing a few comb jellies (Sea Gooseberries) every now and then, but otherwise there wasn't too much today. But just as I was about to leave the beach, a small blob caught my eye.  It was soft and clear, about 2 cm long, with a dark purplish line inside running through the center.  

I picked it up to see what it was.  It didn't look like much at first.  It was covered with sand, and it pretty much collapsed in my hand; that is, it didn't have much structure at all.  But there was a very small, rounded projection at one end...and something was puzzling about this mystery blob.  So I pulled out a small plastic bag, filled it with seawater, and dropped the blob into the water.

Now the sand grains fell away, and I thought I could see some darker speckling on the mostly transparent "jelly."  But I still wasn't certain if it was an entire animal or just a piece of a much larger organism.  

I kept watching, and turning the bag to look at the blob from different angles.  The small projection at one end appeared to get a little larger...and then the most magical thing happened!  Small wings extended out from either side and began to flap!  I knew right away what it was, but I hadn't seen one on Bodega Head yet, and I'd never seen this species.

Here are two pictures in a bowl of seawater:

 

 

This is a pelagic snail commonly called a Sea Angel (Cliopsis krohni).  They belong to a larger group known as gymnosomes ("naked-body," referring to their lack of a shell), a type of pteropod ("winged-foot," referring to their foot being modified into swimming wings).  They swim through the water slowly by flapping their wings.

A diagram will make it easier to see their basic body parts.  Look for the small head with tentacles at the top, the paired, rounded swimming wings at the base of the neck, and the large soft body with internal organs (viscera) visible in the center.

 

Modified from The Light & Smith Manual (2007)

I took a couple of quick photos under the microscope.  The next photo shows the head and tentacles and the extended wings (in motion).

 

Below, an extreme close-up of the left wing shows some intriguing patterning  (muscle bands?).  Note that the wing is not damaged.  Sometimes it would crinkle like that when being retracted, but I watched to see that it appeared to be fine during the next stroke.

 

The surface was covered with dark stellate (star-like) chromatophores and scattered white spots.  Although they look brownish in these photos, I was having a little trouble with the lighting tonight and I would have described them as purplish in natural light.

 

In Pacific Coast Pelagic Invertebrates, Wrobel and Mills (1998) state that Cliopsis occurs north of southern California in temperate waters to depths of 1500 meters.

Cliopsis is a voracious predator that feeds on another pelagic snail called Corolla spectabilis.  Does that name sound familiar?  Last year I posted a few photos of Corolla's gelatinous pseudoconchs.  You can review those posts from August 2012 and November 2012.  

Although I've seen pteropods elsewhere before, I never would have guessed that my first encounter with one on Bodega Head would have started with a small sandy gelatinous blob on the beach!