Box jellyfish
Although the notoriously dangerous species of box jellyfish are largely restricted to the tropical Indo-Pacific region, various species of box jellyfish can be found widely in tropical and subtropical oceans, including the Atlantic Ocean and the east Pacific Ocean, with species as far north as California ("Carybdea confusa"), the Mediterranean Sea ("Carybdea marsupialis") and Japan (such as "Chironex yamaguchii"), and as far south as South Africa (for example, "Carybdea branchi") and New Zealand (such as "Copula sivickisi").
Ada Ciganlija
These anthomedusae begin their life as polyps and develop into jellyfish only if conditions, such as purity and water temperature over 25 °C, are right. However, authorities claim that these harmless and almost invisible jellyfish (they are only to wide, bell is in diameter and have no sting cells) actually have been present in the lake for over 20 years. The first specimens were discovered in 1994 and they can also be found in the Danube. They live only for several days.