UFOs (Unidentified Found Objects ;-)

[paul monfils]

These are shell plates from chitons. Chitons are a separate class of mollusks. Each animal has a series of 8 shell plates, smaller ones toward the anterior and posterior end, and wider ones toward the middle of the body. The shell plates are held together by the girdle, a muscular band that encircles the outer edge of the animal. The ends of the shell plates are embedded in the girdle. The underside of the animal has no protective shell, but it lives attached firmly to the surfaces of rocks or other hard surfacess (often including the shells of other mollusks, dead or alive). When the chiton dies, the girdle and soft parts decompose, freeing the shell plates to wash ashore.

https://www.britannica.com/animal/chiton-mollusk

http://www.bily.com/pnwsc/web-content/Ch...ation.html