Why are there holes through some clam shells?

moonsnailholezd2The shell to the right with a hole through it was hinged to another shell of equal size with an animal living inside (in this case, a clam). Animals with two shells hinged together are known as bivalves. Often, in restaurants oysters and clams are shucked and served “on-the-half-shell” (Yum! I prefer them plain, but sometimes mix it up with ones with plenty of horseradish!).

Animals in the ocean do not have the luxury of someone shucking their prey, but rather use an adaptation called a radula. A radula is the sharp, drill-like tongue of some mollusks (e.g., whelk or conch). Radulas are found on every class of mollusk except for bivalves. A whelk or a conch would use their radula to drill into the clam and then slurp out its meal … Leaving behind a perfectly symmetrical hole. Moon snails and oyster drills are also well-known for using this technique to drill into clams for a feast.

Image (c) imageshack.us


  1. The Other 95% has a video clip of an Oyster Drill using it’s radula and accessory boring organ to drill through an oyster similarly to a moon snail drilling through a clam. Even cooler is the sound of the radula… though for the oyster it must be akin to fingernails on a chalkboard.

  2. timelesslady says:

    Great Post! I am linking to it from my blog this Monday morning.Your post will perfectly explain why some of my seashells have a perfect hole in them. Kathy


  1. […] with another half and closed, with a clam or an oyster inside. Then a mollusk comes along with a drilling-like tongue and begins to drill a whole down into the shell. Then it slurps out the […]

  2. […] On our last late-season trip to the beach I found quite a few clam shells with perfect holes in the top. I love finding clams like these…if I want to string them in a project the holes are already drilled for me. Mollusks of all kinds drill these holes. You can find an excellent explanation of this here: Why are there holes through some clam shells? […]

  3. […] Knobbed whelks feast on clams using a radula. […]

  4. […] (By the way, have you ever wondered why some seashells have perfectly circular holes?  Well, here is the […]

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