Boring Sponge- Cliona celata
This species of sponge is found around the world. This creature creates round holes up to 5cm in diameter in limestone or the shells of molluscs, especially oysters. The Boring Sponge digests its food through an acid digestion technique where it bores interconnecting chambers through limestone and the shells of its meals. It then absorbs the nutrients from the broken down parts of the chambers.
This is a picture of a boring sponge attaching to an unidentified object.