The shell that you can see embedded in this lump of limestone, picked up on the beach at Seaburn last week, once contained the living mollusc known as a wrinked rock borer Hiatella arctica. This remarkable animal settled on the rock and then used the coarse ridges on the outside of its shell to bore its way into the soft limestone. There are five holes bored by separate animals in this rock and they've converted it into the geological equivalent of a lump of Swiss cheese. As rock borers grow their hole enlarges and once they are completely within the rock their future is quite literally set in stone - there's no way they can get out. When they die their shells are often trapped inside, so when I shook this rock it rattled. Piddocks have a very similar life style.........
This is the live animal, in a rock that's been cracked open, revealing the two red siphons that it uses to circulate water through its body. You can see that this individual is a good deal larger than the entrance hole on the left, through which it draws its supply of oxygenated water and food particles that it filters out from the water current.
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