We were at the split yesterday, I was sitting in the water by the picnic tables and happened to nudge a small patch of moss that was actually a jellyfish,upon inspection of the area I found over 30 of these green oval patches of moss like spots on the sand bottom to be what are called upsidedown jellyfish. Thinking mabe they have always been there I just never noticed. I googled them, yes I got stung but very minor for how invasive I got with them. Their sting is mild unless you are allergic to bee stings etc. Check them out, they lay on the bottom in the shallow water around the picnic tables that are in the water, about the size of the bottom of a coffee cup. They look like a clump of grass. Take a stick and flip them over and then you can see the jellyfish...I actually thought they were pretty kool...

I saw a whole lagoon full of various ones out at Turneffe. Really beautiful.

Anybody have a photo of these? I am extremely allergic to bee stings and would not want to step on one!

The lagoon within Reef Village is full of them. Look from the bridge to the pool island and you can't miss them. Impressive sight. There are all sizes from a few inches to nearly a foot in diameter. I used to think they were anemones until you see them actually pulse and move about.

Yes i have seen them in multitudes in the san pablo,canals and laggons. Very pretty.

This will get you to some photos.
http://www.reefguide.org/carib/mangroveupsidedownjelly.html

They are always at the Split, but in small numbers, and they try to hug the bottom, so they don't usually hit swimmers. Only if the current is especially turbulent do they get ripped loose and then tumble about helplessly, and may give you a mild spot of rash if they bump into you. Or if people misguidedly kill them, then the dead ones flop about in mid-water and are more likely to sting someone. Jellies are an important food for eagle rays, whale sharks and many other marine organisms!And upside-downs are fairly harmless. Pour vinegar over the sting right away, or use hot water later, and you'll hardly notice the spot the next day.

Outside of that one day I have not seen anymore at the split. Been gong to the split about 2 days a week for 10 years..now i am always lookng for them, not as a threat but but just curious. They are pretty harmless.