Here in the Swan River in summer we get a huge amount of these ugly creatures. Often 20cms across and 15cm deep body. In quiet conditions you can feel the rudder hit them on my little boat. When swimming you tend to do breast stroke. Totally harmless the kids are often terrified of them. I was led to this story or research on them and found it fascinating. Takes a bit to read it all though. Turns out they give up their stinging carnivorous ways when tiny juveniles attached to rocks and about 1mm sized. They become homes to and live on algae that provide food and oxygen from sun light. Makes me quite fond of them. Ugly is beautiful. ol'will