Or perhaps a tunicate?
About 1/4", bell looks like a child's drawing of the moon if the moon was made of clear goo. "Portholes/craters" ringed with white dots. Seems to have several long hairy tentacles like a gooseberry or other comb jelly, but the bell doesn't seem to have comb plates.
In the canals near the city of Aveiro, Portugal. Relatively large.
Fled to Hadley to escape the nettles in Tarpaulin Cove. Found them here as well.
Less abundant this year. I'm told they are preyed on by Chrysaora quinquicirrha, which are abundant this year at this time.