This image has been sitting in the unidentified category since February, I think it is better to confirm to the category that you are certain rather than images sitting in the unidentified category, I am sure this is Pyura sp.. Feel free to change it to P. australis if you want.
I deleted the earlier comment after a more careful look. It still looks like the P spinifera in Edgar p 436 and they have been photographed at Potato Pt.