This was in our Marina today.
Not sure why the photo is on its side...
Cant see it on a google search and wondered if anybody on here knows what it's called?
Its around the size of a large dinner plate and has a deep blue almost purple outer frill which moves up and down as it swims.
Crystal Jelly maybe
jellyrisk.eu/media/cms_page_media/115/27.Jellyfish%20Guide%202014%20-%20Spain%20(english).pdf
Based on its similarity to a Ming era dinner plate I think you have just spied the rumoured ,newly developed, Chinese marine surveillance drone, a cunning fusion of biological and electronic technology. Devilishly clever what!
I spotted a box jellyfish while kayaking on Lake Macquarie about 5 yrs ago. Called the local council and no one believed me.
Then on their website about 4 months ago was a story about a box jellyfish washing up on shore and how unusual and dangerous it was to be so far south!!
I recommend giving the council a call if it is something unusual. At least you have the picture to prove it.
Select to expand quotejacktheflyer said..
I'd call it Jim the Jellyfish.
In view of the time of the year, with all the festivities and all, I'd call im 'jellybelly'...a migratory species which usually makes a yearly appearance, but by all official accounts is increasingly said to be endemic.
Hails from Queensland, bounces around not really knowing which direction to go, dressed in blue, have to call it Peter. 
