Complex sentence: The shell of this species is well-known to beach-goers in the northeastern USA, who often look for empty shells of this species to dig with, or take home to use as decorative dishes or ashtrays.
Split into simpler sentences: The shell of this species is a very well-known object to beach-goers in the northeastern USA. People often look for the empty shells of this species, either to dig with, or take home to use as decorative dishes or ashtrays.