text: There is a marine flatworm named Pseudoceros dimidiatus, that lives in the seas around Bali and Indonesia.  I imagine that is the critter you are refering to.\n\nIt doesn't really have a common name though.  I guess the only ones who care about marine flatworms are people who use the scientific names.\n\nIt is a very attractive marine flatworm though, jet black with blazing yellow stripes.  Very pretty.