Surely one of the most beautiful British marine molluscs, the living Necklace or Moon Shell, Polinices catenus (da Costa), is shown here washed up on the sands of Rhossili Bay, Gower, South Wales.
This gastropod is a carnivorous predator that inhabits the lower shore. It often ploughs a furrow in the wet surface sediments at low tide level as it travels around on incoming tides, searching for small bivalved molluscs on which to feed. It drills through the shell of its prey making a neat circular hole through which it can eat the flesh. The hole is almost invariably drilled near the umbo or hinge area of the valve. It particularly likes to eat Thin Tellins (Angulus tenuis), Banded Wedge Shells (Donax vittatus) and young specimens of Striped Venus Shells (Chamelea gallina).
The photograph below shows the other side of the same living Necklace Shell. The brown chitinous operculum (lid) is visible in the shell opening or mouth where the animal has withdrawn into the cavity of the shell and sealed itself safely inside.
This species of gastropod mollusc derives its name from the shape of the egg masses that it lays. These look a bit like a torque type of necklace – a broad open curved band of eggs.
Revision of a post first published 15 May 2011
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Jessica's Nature Blog 
This is very similar to the Northern Moon Snail that I frequently find on the beach here in Nova Scotia. They’re very beautiful shells. Their egg cases are certainly unusual.
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Moon Snails belong to the same family as the Necklace Shells – Family Naticidae. It took me a while to realise the ‘necklace’ name referred to the egg cases and not the shell.
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Very old post I know but I was wondering if in fact the name ‘necklace shell’ comes from the small holes that the animal drills into its prey, meaning that their shells are ready for stringing onto a necklace. Otherwise it is very difficult to make a hole in a shell without it breaking – unless you have a drill which was probably not commonplace when the necklace shell was named. Just my thought on it that’s all.
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I have always thought that the common name of Necklace Shell referred to the egg masses that this species lays. It is common to find the almost circular bands on the beach although the eggs that are initially attached to them (the beads!) are usually missing.
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