TYBEE BEACHCOMBER | DEC 2018 25
MOON SNAILS &
HOLES IN SHELLS
If you do much shell collecting on Tybee Island, one of the things you quickly notice is that
many of the bivalve shells have a nice, neat, round hole in them. It’s not a chip or broken place,
but is a perfectly round, smooth, beveled hole. It’s just right for making a necklace.
Those holes were not original features of the bivalves (clams, cockles, Arks, Coquinas) that
produced the shells. Those holes are the result of the activities of certain snails. And it is one of
those snails, the Moon Snail, that I want to discuss this month.
Moon Snails, also called Shark-eye Snails, are fairly common on Tybee’s beach, usually
burrowing under the wet intertidal sand. Because they are normally an inch or so deep, their
subtle trail and bump are often overlooked until you know what to look for. But their empty shells
are among the most common Gastropod (snail) shells that we find shelling on Tybee. The shell is
generally round, light brown, and has a wide round opening or aperture.
When burrowing through the wet sand, the Moon Snail is hunting for food, particularly for
bivalves that live in the upper layers of the sand. While burrowing through the sand, the Moon
Snail’s body will extend out through the shell opening, and it will use its muscular “foot” to plow
through the sand. If you find a live one, place it in a container of seawater for a few minutes and
it should open up and start gliding around. You will be amazed at how big its body is when it is
extended out of its shell, and you’ll wonder how all that body can fit back into that small shell.
When it locates a bivalve down in the sand, the Moon Snail wants to eat the meat inside the
two shells, but the Moon Snail doesn’t have any way to pry the two shells apart. But what the
Moon Snail does have is a tongue-like structure inside its mouth called a radula. The radula is
hard and has rows of numerous small sharp teeth-like structures, so it is like a file or rasp. It will
extend that radula out and drill a hole through the clam’s shell. It probably also secretes an acid
substance that helps soften the clam’s shell and makes the drilling easier and faster. Once the
hole is drilled, the Moon Snail extends that radula and proboscis through the hole and inside the
clam where all the meat is. Down inside there, the radula is used like a knife or food chopper
slashing around, and it chops up the meat and makes soup out of it. And then the Moon Snail just
slurps it out through the hole!
So that nice neat hole in the bivalve shell wasn’t part of the original design of the clam that
made that shell. Instead, that hole was pretty much the last thing that happened to that clam’s
shell! So you can probably thank a Moon Snail for drilling that hole in that shell for you.
Dr. Joe Richardson (Ph.D. Marine Sciences) is a retired marine science professor with 40 years
of research and teaching experience along GA, the southeastern coast and Bahamas. Besides
research, he conducts Tybee Beach Ecology Trips (www.TybeeBeachEcology.com) and frequently
posts pictures of their findings on his Tybee Beach Ecology Trips Facebook page.
Beach Walks
with Dr. Joe
By Dr. Joe Richardson
/(www.TybeeBeachEcology.com)