ShellSanibel
Read the beach.
Lightning whelk
Sinistrofulgur sinistrum formerly Busycon contrarium, Busycon sinistrum
common · 4–12 in (10–30 cm); occasionally larger
How to tell it
The one that opens on the left. Hold it with the spire up and the aperture faces your left hand — almost no other shell on this coast does that. Young shells carry the fine brown axial streaks that give it its name; large old ones are often chalk-white and worn smooth.
What it gets confused with
Every other large whelk and the true conchs open on the right. If it opens right it is not this. Horse conch is right-handed and turns orange inside.
Where it turns up
Gulf beaches after a blow, and along the wash at Blind Pass. Big ones tend to arrive broken.
Alive or empty
A live one is heavy, sealed by a dark leathery operculum, and often has the animal’s foot visible. Empty ones are markedly lighter and dry inside.
Worth knowing
The Florida state shell, and the largest thing most people will pick up here.
Taking live shells is prohibited in Lee County
That includes anything with the animal still in it, and sand dollars, sea stars and urchins whether or not they look alive. If it moves, if it closes, if it is anchored to the sand — put it back where you found it, the right way up.
A shell with an animal in it is not a souvenir that has been left out. It is the animal’s house, and the beach is not producing spares.