While collecting sediment-dwelling animals from the bottom of the lough, we were puzzled to find an animal living in a snail shell that was obviously not a snail. It appeared to have a long tube-shaped appendage that was constantly everting and retracting from the shell aperture.
Our colleagues at University College Cork helped us identify this mystery animal - it was a sipunculid, also known as a peanut worm. This species, Phascolion stombi, is often found inhabiting snail shells and worm tubes. In this case, we found the sipunculid living in a Turitella communis shell (also known as a tower shell).The tube-shaped appendage of the worm is called the introvert, on the end of which is the mouth. Often sipunculids have a characteristic introvert-withdrawing behavior, which is what helped us solve the mystery.