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.

Photo credit: Fogonazos