 The tawny nurse shark has few natural predators ; attacks on this species have been reported from bull sharks ( <unk> <unk> ) and great <unk> ( <unk> <unk> ) , while the related nurse shark has been known to fall prey to tiger sharks ( <unk> <unk> ) and lemon sharks ( <unk> <unk> ) . Known parasites of this species include five species of <unk> in the genus <unk> , which infest the shark 's spiral intestine . 
