Okay, I'm 99% sure I have this now. Searched through the Internet for about an hour this evening and pretty sure it's a Polycarpa Pigmentata - otherwise known as a sea squirt.
Amazing animal and apparently very closely related to human's ? Has a heart which beats about a hundred times with blood flowing in one direction. The heart then stops for a while and when it restarts the blood flows in the other direction.
Can this be true ?