Latin for Little Door!

Moon snail operculum on the left and knobbed whelk operculum on the right!

What are these two pieces of thin shell? Well, these are called operculums. They are usually found attached to different sea snails, like knobbed whelks or moon snails. Operculum is Latin for “little door,” and as you can imagine, the job of an operculum is to protect the sea snail that lives within its shell! The operculum acts like a trapdoor, sealing the opening of the snail’s shell when it retracts inside. This helps prevent predators, parasites, and even drying out when the tide goes out. Operculums can vary in shape and texture depending on the species—some are flat and circular, while others are more claw-like or spiral-shaped. It’s a clever natural defense system, and a fascinating little piece of marine armor! 

*Note that on most bony fish the plate covering their gills is also called the operculum. It has a similar function to protect the gills but is different in shape and composition.*