This shell has been bored by polychaete worms.
Bivalve Sanibel Island, FL Dec. 16, 2009 I found this live animal on a sandbar at low tide. It can bury into the sand with a strong foot. Clams are filter feeders that pull water into their body through one siphon and expel it out the other siphon.
A small sample of the mix of shells on Sanibel Island's beaches. Sanibel is a beachcomber's paradise! :) It is the best beach in America and the 3rd best in the world for shells. Most of the shells are halves of bivalves since they are preyed upon by the single-shelled gastropods, crabs, sea stars and other animals.
