I love exploring tidepools on the beach! One of our most common live animal finds is the moon snail. Also known as the shark’s eye shell, Neverita duplicata (formerly known as Polinices duplicatus.) At low tide, you can find their furrows in the tidepools and sometimes find them cruising for prey. We usually find them with coquina shells.
Moon snails are univalves (one shell) that plow through the soft sands of the swash zone. They are gastropods, (literally stomach-foot), and when they are moving through the sand, most of the shell is completely covered by the snail. (Which is why recently dead snails have very shiny shells.) The front part of the foot is used for digging, and the mantle surrounds the shell to streamline the shape and allow it to move through the sand, below the surface. The foot takes in water to expand and propel the snail through the sand. When disturbed, the moon snail expresses that water and withdraws the foot into the shell, closing off completely with an operculum.
These molluscs have a radula, a sort of toothy-tongue apparatus, which can be used to bore a hole into the shell of a bivalve. The snail also secretes an acidic solution, which helps dissolve the shell of the prey as well as with eventual digestion. (A naturalist once described this operation to us as “lick-n-spit”.) Here, we interrupted a meal– you can see the coquina clam, helpless against the onslaught, has almost been bored through by a moon snail. The “jewelry shells” you find on the beach with perfect holes were likely preyed upon by a moon snail or similar gastropod. In our tidal sands, we most often find them with coquina shells, but they are also cannibalistic. You may find moon nails shells on the beach with the tell-tale drilled hole. Other predators of moon snails include sea stars.
Moon snails also leave evidence of egg laying on the beach. Their egg cases are called sand collars and are frequently mistaken for plastic trash on the beach. Eggs are laid in a round collar cemented together with sand and mucus. As with other egg cases, you may be able to see where the young snails hatched. We found this one on the beach. Upon closer look, you can see the tiny snails and even where they hatched out.
Moon snails and their shells also provide valuable real estate of other beach organisms. Hermit crabs move onto their shells, and anemones sometimes attach to the hermit crab shell.
There are more photos in the slideshow below: