The bristle worm Polydora ciliata is a small tube worm. It makes short U-shaped tubes from mud. This worm can burrow itself into stones, chalk and limestone, muddy bottoms and even shells. Due to the massive amount of worms living on stones at the foot of dikes around the low-tide waterline, it can be very slippery from the layer of muddy tubes. If the worm is underwater, it will stick out its two thin tentacles to catch food. There are various species of these bristle worms which are practically identical.