Rocks with holes made by Piddocks 8 – Empty Common Piddock shell in rock burrow showing the long curved internal processes, called apophyses, projecting from beneath the umbone, which serve as extra muscle attachments to aid the drilling process. Apophyses are easily detached and therefore rarely seen in beach-worn shells washed ashore. Monmouth Beach in Lyme Regis, Dorset, England.
Jessica's Nature Blog 