Also known as Blue Button, Blue Button Jelly, Disc Hydroid, Stinger, Stinging Bluebottle.
Found near the surface, drifting in bays, estuaries and lagoons also out in the oceans, moving with the currents, tides and winds. They are often blown ashore in bad weather. The round hard float is almost flat with stinging strands of hydroid surrounding it, each strand has little branchlets off, they do not give a powerful sting, more of an irritation.
They feed on zooplankton.
Length - 3cm
Depth - surface of the water
The blue button is preyed upon by the Glaucus atlanticus - Atlantic Glaucus:- http://www.whatsthatfish.com/fish/atlantic-glaucus/1984 They drift along with them feeding off their tentacles!
These are not true jelly fish they are Siphonophore a colonial organism made up of zooids.
Jellyfish are 95% water.
They have no heart, brain, blood, or gills. The body of the Jellyfish is called a bell. They do have a mouth, tentacles and arms around their mouth. They use their arms around their mouth to help sense and find food that ends up inside their mouth. Ref: https://en.wikipedia.org/wiki/Porpita_porpita