Original: Its coiled castings are a familiar sight on a beach at low tide but the animal itself is rarely seen except by those who, from curiosity or to use as fishing bait, dig the worm out of the sand.
Simplified: Lugworms make the coiled tubes of sand that are a familiar sight on a beach at low tide but the lugworm itself is not seen except by people who dig them up from curiosity or to use as fishing bait.