BPMN message flow link

Yes but did you put tasks in different pools? Only if tasks are in different pools and you connect them then you will have message flow link (link.category = "msg’ and it is dotted and has circle on start and arrow at the end) instead of sequence flow link which is full line with arrow at the end that you describing. So you have to put tasks in different pools not different swim lines or the same swim lanes to get links I got in my picture.