Lion's mane jellyfish (Cyanea capillata) larval stage. This is the ephyra larval stage. When fully grown, this is the largest known species of jellyfish. It can reach over 2 metres across with tentacles of around 30 metres long, containing millions of nematocysts (stinging cells). This jellyfish ranges from Arctic waters to the coasts of Florida, USA, and Mexico. Photographed in the Russian Arctic, in the White Sea.