Something colorful, something new

On 15 September, Eric and I noticed some very small scallop shells washed up on Salmon Creek Beach.  Here's an example:

 

We were impressed with the diversity of shell colors and patterns:

 

Pick your favorite!

 

 

These are juvenile Rock Scallops (Crassadoma gigantea).  Not only did we discover how diverse their shells can be, but by looking at them up close, we learned something new.

 

Did you notice the row of teeth below the hinge?  (To me, it almost looks like a line of small arching waves.)  This feature is called a ctenolium.  The teeth guide the byssal threads that the scallop uses to attach to the substrate when it's young.

 

O Sole Mio

Are you ready for your next mystery close-up?  Can you guess what this is?

 

I'll zoom out a little more: 

 

Do you have an idea now?

How about if I zoom out even a little further?

 

Can you tell that this animal has two shells (or valves)?  And that it's just starting to open up and to extend its tentacles outward?

Warning: If you haven't guessed yet, the next photo might give the answer away.

 

Yes!  This is a scallop, specifically a juvenile Rock Scallop (Crassadoma gigantea).  And those small black dots lining the margins of the shells are its eyes — lots of them!

If you look at a cross-section of a scallop's eye, you'll find a cornea, a lens, a double retina, and a concave mirror that reflects light back to the retinas.  This illustration will help visualize those structures:

 

Modified from Speiser, D.I., E.R. Loew, and S. Johnsen.  2010.  Spectral sensitivity of the concave mirror eyes of scallops: potential influences of habitat, self-screening and longitudinal chromatic abberation.  J.  Exp.  Biol.  214: 422-431.  [This figure shows the eye of a Sea Scallop, Placopecten magellanicus.  The scale bar represents 0.1 mm.]

Some research has been done into scallop vision.  It's thought that scallop eyes can probably detect large moving objects (such as predators), and possibly nearby habitat characteristics as well as food particles moving by in the water.

The next image shows the entire animal.  It was only ~1 cm across.

 

This small scallop was the star of a recent music video produced by Eric during his Invertebrate Biology class.  I can't help but sing the praises of this wonderful footage of a scallop in action!