Flat-tip Piddock (Penitella penita) siphons are the only evidence of this clam that bores into soft rock. It begins to bore as a very small animal and continues to rotate and enlarge the hole as it grows. It is literally trapped in its home since the original entrance is much smaller than the adult clam. These bivalves are responsible for substantial erosion along rocky shores in their range from Chirikof Island, Alaska to Baja California, Mexico. The siphons serve for respiration, reproduction and food gathering, one for intake and the other for exhaust.