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Moon Snails and Clams

Moon Snail and Small holes in a Clam Shell that I found on the beach this week:



If you "google" the question "what are the perfectly round holes on clam shells?," you learn that they are made by Moon Snails.  They make this hole with their sandpaper-like radula in the same place on each clam, after excreting something to soften the shells.  Then they suck out the clam for dinner. 


The radula is part of the mouth, and for those who are interested, google "radula and/or mouth of moon snail" images.  The foot can be extended from the shell, as in the above photo, and cover the clam.  It also spreads out over sand, secretes mucus, and lays hundreds of eggs in the mucus.  The snail then detaches from the sand leaving behind a round, rubbery looking structure which can be found on beaches - usually in several pieces.  One year we saw so many on the beach and didn't even know whether they were manufactured or animal.

NOTE: THIS MAY BE TOO MUCH INFORMATION - but this is the blog entry and photos from our search for the origin of these "sand collars."

June 2013 Huge Beach Mystery: Early this week we arrived for our early morning 2 mile walk and saw many unusual "objects" on the beach. They were very smooth 6-8 inch beige partial circles, each with an identical lip and curved shape which resembled a piece of a toilet plunger.  None of them were a complete circle.  Were they pieces of rubber, manufactured as gaskets?  If so, why were there so many at the high tide line - extending over several miles.

Here are a few photos.  Wet they were very flexible and felt like leather or rubber.  Dry, they were very fragile and crumbled easily.  In the first photo you can see the size relative to an adult hand.



We picked up a few each day during our walk and asked random people if they could identify these strange things.  Surprisingly, most people hadn't seen them although they were everywhere.  Others, including those who lived here their entire life, had no idea what they were.  In each instance, the first question was "do you think they are organic or machine made?"  Each day we did some random computer searches and found nothing.  Our best guess was some part of ocean seaweed, but what? 

Yesterday I was looking at kelp images and saw a link to a website called MarineDetective.  What could I lose by emailing this Vancouver BC diver and marine expert.  So I did.  Within 30 minutes I received this reply.

"Laughing here! I get asked this so often. These are the egg cases (aka egg collars) of Lewis' moon snails ( Polinices lewisi)!  Moon snails are big predatory marine snails. They look so human made that I have had to correct people when they pick them up thinking they are garbage! By a remarkable method, the female moonsnail forms one layer of the collar by gluing together sand grains with mucus; then the fertilized eggs are laid on this layer and THEN she seals them in with another layer of sand and mucus!!!  The eggs are held within the collar for 1.5 months and, in the ones you found, may already have hatched out to be 1000s of planktonic larvae. I include a more detailed description below." 

Best wishes!
Jackie Hildering
Biologist / Marine Educator
Follow "The Marine Detective" at http://www.themarinedetective.ca/ 


The miracles of nature. This will be a very busy summer. My son and family are moving here from Ohio. My husband is in like for a focus beam treatment at Stanford to stop his essential tremors. Figure Drawing show for the month of June.
Enjoy your beachy summer!

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