Freshwater Jellyfish
Craspedacusta sowerbyii

Did you know Southern Indiana has jellyfish?
They can be found in Yellowood Lake every few years.

Here are some references and pictures of them

 

Tom Pelletier's article from 2001.
Gen-yu Sasaki's great page with pictures and explanations.
Here's a nearby page on "Things that don't belong where they are."
Dr. Terry Peard at Indiana University (of Pennsylvania!) collects information and has a very good web page about these.
A Boise, Idaho Girl Scout troup found some jellyfish.
Encyclopedia Brittanica article.
The US Geological Survey page, which explains where these jellyfish came from, and has a map of where they're found now.
A Google Search for "Freshwater Jellyfish".
Getting off topic a little, in 2017 there's a similar saltwater phenomenon happening in strange numbers. "Pyrosomes", which are colonies of zooidsa>.