Umbrella shell - Umbraculum umbraculum

Descrission:

The umbrella shell lives in Australia and as far afield as Madagascar. It would have to count as one of the strangest-looking molluscs in the sea. Its shell is a remnant flat structure on top that doesnt do much except provide a home for algae. The animal is covered in wart-like nodules that arent pretty but provide excellent camouflage. Divers can often swim right past one of these, even though they grow quite large up to 8 cm across. This one is out and about, so you can see the oral tentacles (chemical receptors) and tiny eyes (light receptors).