Apple Snails: Family Ampullariidae
The Apple snails are a fresh water snail that sometimes ends up in salt water. According to Harry Lee: "They probably reached the beach after being flushed out to sea incidental to a flooding event. See the extensive treatment at <The Channeled Applesnail In Northeast Florida (jaxshells.org)>."
I have collected two types: Channeled Apple Snails (Pomacea canaliculata) Lamarck, 1822 and Florida Apple Snail, (Pomacea paludosa) Say 1829. Both types were collected at S. Hutchinson Island Beaches. The Channeled Apple Snail is an invasive species native to South America.