The Sand Collars of The Moon Snail

These strange-looking frilly edged flat spirals made of sand sometimes wash ashore on tropical beaches. They are called sand collars—so called because they are said to resemble an old-fashioned detachable shirt or blouse collar. Sand collars are made by the female moon snails when they lay eggs.

Moon snails, also known as the necklace shells, are a predatory sea mollusks in the family Naticidae. The snails are known for their rather globular-shaped shells and their voracious appetite for other mollusks. When a moon snail finds another snail it wants to eat, it wraps its huge foot around the hapless prey and drills a hole through the victim’s shell using its radula—a tongue like structure— and an acid secretion to soften the shell. Once the shell is bored open, the moon snail proceeds to consume the flesh of the prey.

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Photo credit: Fogonazos

When a female moon snail is ready to lay her eggs, she sinks to the bottom of the ocean floor and begins to collect grains of sand with her foot. Then using mucus, she cements the sand grains together to form a flexible collar. The snail lies at the center of the collar as she creates it, so the hole in center of the collar gives an indication of the size of the mother snail.

The female lays her eggs inside the collar and spreads it evenly around the structure. A second layer of sand and mucus protects the thousands of eggs contained within the sand collar. When finished, the snail leaves the sand collar by digging into the sand and moving away from underneath it.

A sand collar that’s intact still has eggs inside. After the eggs hatch, the collar breaks allowing the newly hatched larvae to escape from their capsules and swim freely towards the open ocean.

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Image credit: www.asnailsodyssey.com

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A somewhat damaged sand collar of Euspira catena. When the light is shines through the collar, it is possible to make out the individual egg capsules within it. Photo credit: Hans Hillewaert/Wikimedia

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