Simplify the following text for a Grade 7 native English-speaking person.
Original: Irukandji jellyfish are tiny and extremely venomous jellyfish that inhabit marine waters of Australia , and which cause symptoms collectively known as Irukandji syndrome .
Simplified: The Irukandji Jellyfish , Carukia barnesi , is a species of jellyfish . It lives in the waters of northern Australia .