Chiropsalmus quadrumanus
Chiropsalmus quadrumanus, commonly known as the four-handed box jellyfish, is a species of box jellyfish found in the western Atlantic Ocean, the Gulf of Mexico and the Pacific Ocean. The sting is venomous and dangerous to humans, especially children.
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.