Phyllorhiza punctata
Photo courtesy of Harriet Perry
Phyllorhiza punctata Australian spotted Jellyfish. Was found in the northern Gulf of Mexico in 2000.  It is suspected that a weather event or change in the Gulf currents brought this jelly to the northern Gulf from the Caribbean.  Gets to 20 inches across.
Indigenous to Indo-Pacific.
Introduced to Mediterranean, Hawaii
Introduced to the western tropical Atlantic late 1960s / early 1970s
Until recently, primary Atlantic concentration in southern Caribbean