My daughter and I stumbled upon this Lion's Mane or "Red" Jelly at Hammonassett State Park today. This species and the Portugese Man-o-war jelly reportedly have the most serious stings. In general, the brightly colored animals (especially red ones) are the more toxic ones, and I instinctly gave this one a wide berth. Update 7/3/2008: Short Beach in Stratford was just covered in small versions of this jellyfish today, from 1 inch to 5 inches in diameter. I was told a couple days ago, the water was filled with very large ones, over one foot in diameter (the one on the photo from Hammonassett was maybe 6 or 8 inches). I've never seen these at Short Beach before.
On a lighter note, the park was a step away from Watership Downs with over a dozen rabbits along the park road on the way out. This one was just stretched out and relaxin'.