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SHELL SEEKER: Shark eye with necklaces

By Staff | May 28, 2010

At the end of my favorite shelling beach in Cape May, New Jersey, there was

a little man-made jetty.  Boulders were strategically placed to build up an

area of beach eroded by a hurricane. It was there that I witnessed

perplexing sea gull behavior.  At low tide the gulls would swoop down and

grab something off the beach.  Then they would fly over to the jetty,

hovering at just the right height, and let their parcel drop to its doom,

crashing against the rocks.  Then, once again, the gull would swoop down and

make a pass at the sandy area adjacent to the rocks, grab its prey and

devour it on the spot or move to higher ground if harassed by fellow gulls

anxious to share their meal.

As always, I looked to by grandmother for an explanation for this bizarre

behavior.  She took me by the hand and we walked over to the jetty covered

with “shell bones,” many of which were bleached white by the sun.  She

explained that the shark eye or moon shell as it is called by some, was a

favorite delicacy for the gulls and that the “rock dropping” exercise made

it possible for them to obtain the “meat” inside the shell.

The Neverita duplicata is found on sandy shores just below the low

tide-line.  It is shaped like a globe, has four to five whorls, and is

generally grayish brown in color. There is a bluish dot in the center of the

top-side of the shell which resembles the iris of an eye – hence its name.

They are a flattened shell and wider than they are tall. Shark eyes are

found from the New England states to Florida and other states along the Gulf

of Mexico. 

Shark eyes are predatory, with bivalves providing the mainstay of their

diet.  Once prey is discovered in the sand, the snail wraps its foot around

the prey and begins drilling a circular hole into the shell, allowing the

soft tissue within to be sucked out and eaten.  Secretions from an accessory

boring organ appear to soften the shell of the prey. The boring process is

very slow, taking from several hours to a day or two.  One of the snail’s

favorite foods is the coquina clam.

Shark eyes are a type of moon shell.  Moon shells are found in all of the

seas of the world and can grow up to three inches in diameter.  The living

snail is amazing looking, with a foot that extends out around the entire

shell.  This flattened pad of flesh is the animal’s means of locomotion.

Flesh from the top of the foot actually folds back over the head, serving as

protection as the foot drags the body through the sand.  Their

well-developed burrowing ability contributes to their survival.

Female moon snails attach their eggs to necklaces or “sand collars,”

circular masses of sand grains stuck together.  The eggs are laid in a

sticky mass of clear jelly substance which is molded over the shell, giving

it the shape of a collar.  The mucus is rubber-like while in the water but

when it gets onshore it becomes dry and brittle.  The sand falls off at the

hatching time and the eggs become visible.