Polinices duplicatus Say, 1822
Shark's Eyes are a type of Moon Shell. Moon Shells are found in seas all over the earth. They are carnivorous gastropods (snails) which burrow in sand or mud. They feed on smaller snails and clams by drilling through the shells of those creatures. The Moon snail secretes an acid onto the victim's shell, then pierces the softened spot on the shell with its radula (a fleshly, toothed tongue). One of the Moon Snail's favorite foods is the Coquina Clam.
The Shark's Eye (or Atlantic Moon Snail) is a bluish gray-brown color with a dark “eye” at the tip of the spire. It might be as much as 3 inches in diameter. The living snail is rather amazing looking, for it has a foot which extends far out all around the shell. The snail can even envelope its shell in this muscular extension of its body.
Julia E. Rogers wrote about Moon Shells in 1931. Her graphic writing is still a joy to read:
No adornment is to be seen upon the strong house that shelters this businesslike mollusk butcher. He rolls up his sleeves, so to speak, and goes after his prey in dead earnest. Put one in a tank of sea water, with sand in the bottom, and before long he recovers his equanimity, and unlocks his door. The amount of foot he unfolds is a matter of amazement when the size of the shell is taken into account. A flattened pad of flesh three times as long as the shell's diameter, and half as wide as long — this is the burrowing, gliding organ of locomotion. In shape it is somewhat like the bottom of an old-fashioned flatiron; the broad, truncated end is forward. A fleshy band on top of the foot folds back over the head, protecting it as the burrowing foot drags the body rapidly after it through the wet sand. The eyes are wanting or buried under a thick epidermis.
This blind, mole-like mollusk finds plenty to eat in the zone just under the surface of the sand. Clams and other shell fish are there. Down comes the hood from over the head when a victim is met. The long proboscis is set, and the radula it contains soon has a neat round hole drilled in the shell, through which the soft parts are extracted by the sucking mouth of the bloodthirsty Natica.
The eggs are laid in a sticky mass of clear jelly which is moulded over the shell; this explains its peculiar collar shape. There is but one layer of egg cases, arranged in regular quincunx order. A layer of fine sand covers each side of the collar, making it about the thickness of an orange peel. While this remains in the water the mucus is rubber-like, and the eggs are safely concealed under the protective film of gray sand. Cast ashore the sand collar becomes dry and brittle. Who has not seen these collars, six inches in diameter and open at one side, lying on the beach? It is useless to try to carry one home without having it shattered. Near hatching time the sand falls off, and the eggs become visible.