Most familiar to me are the soup plate sized red-brown ones common in Southern Tasmanian waters and also the little bean shaped crystal clear ones I have only ever seen on beaches. They are simply too transparent while in the water to be visible.
I did do some research, out of interest and discovered that all jellyfish are gelatinous zooplankton, but not all gelatinous zooplankton are jellyfish...there you are.
I read recently about a jellyfish app. that has been developed locally, we have a well known jellyfish expert, Dr. Lisa-Ann Gershwin living in Tasmania who has been working with others on its development. It will be very useful to families, fishermen etc to anyone who gets a sting.
Some of our tropical jellies are lethal...there have been a few strange diving fatalities in past years which have been identified as being caused by the irukandji, a very small but very poisonous box jellyfish. An adult is only about 1 cm long, but may trail up to a metre of tentacles. It's sting is reputed to be around 100 times more more venomous than that of a cobra...one to avoid if you are lucky enough to actually spot it coming...
The frame and the inchies to date are now off to the framer to be sorted...hopefully! I think it will be a bit of a challenge for them...