Riddle of the collars of sand
A family walk along a Devon beach turned into a game of guess the mysterious object, writes Charlie Elder
AWANDER along a Westcountry beach at low tide always offers the chance of a surprise find or two – from the skeletal remains of buried wrecks and washed up plastic toys from past decades to assortments of shells and the scattered mounds of stranded jellyfish.
But mysterious shapes in the wet sand during a visit to North Devon at the weekend had me and my family scratching our heads.
Exposed by the outgoing spring tide along the lengthy beach at Westward Ho!, the horseshoe-shaped semi-circles looked as if they could be either natural or man-made.
There were hundreds of them, each sitting in a small pocket of water close to the low tide’s edge – leathery to the touch with a grainy and gelatinous appearance that gave few clues as to their origin.
I guessed that they might be the disintegrated remains of jellyfish, or seaweed, or perhaps material offcuts that had somehow found their way into the ocean and drifted on the currents before being strewn along the sandy bay.
The answer turned out to be just as intriguing.
They are actually known as sand collars and are the creation of moon snails, which deposit their eggs in a curled flattened mix of jelly and sand.
Moon snails live in sandy habitats and these egg masses, the shape of a collar, can contain thousands of eggs within the matrix.
Back in May 2020, people reported finding these sand collars in Whitsand Bay, near Plymouth, and Geoff Wigham, former associate professor of marine biology at the University of Plymouth, explained their origin.
He told WMN sister-website PlymouthLive at the time: “Eggs are laid in capsules, many thousands of which are embedded in a collarshaped mass of jelly, shaped by the animal’s foot and hardened and strengthened by the incorporation of sand grains.
“Each individual capsule may contain many eggs, of which most are ‘nurse eggs’ providing sustenance for the one or two that will eventually hatch from each capsule as juvenile snails.
“The collars, or necklaces, are laid on the surface of the sand, their production peaking in spring and early summer, and are often washed higher up the shore by wave action. This is particularly so following periods of rough sea conditions.”
He said the size of those found in Whitsand Bay indicated they were likely to have been created by a species of moon snail called Euspira catena – a predatory marine snail which can grow to about an inch across and feeds on bivalve molluscs, penetrating their shells and sucking out the contents.
Those I came across with my family over the Easter weekend at Westward Ho! looked to be the same size as the Whitsand finds, so everything points to them also being the work of Euspira catena.
Dr Wigham added: “The common name ‘Necklace Shell’ derives from the appearance of the collar-like egg mass, while ‘Moon Snail’ refers to the semi-lunar shape of the opening of the shell.”
Our animal, mineral or vegetable conundrum solved, I look forward to the next brainteaser washed up by the sea...
‘Eggs are laid in capsules, many thousands of which are embedded in a collar-shaped mass of jelly’