Ingo Arndt / Mastigias jellyfish (Mastigias sp) with mass of jellyfish in background, Jellyfish lake, Palau, Western Pacific Islands, Micronesia

Ingo Arndt / Mass of Mastigias jellyfish (Mastigias sp) in Jellyfish lake, Palau, Western Pacific Islands, Micronesia, March 2009

Alex Mustard / Aggregation of Golden jellyfish (Mastigias sp.) in a marine lake in Palau, the golden colour of this species comes from symbiotic algae in its tissues. Jellyfish Lake, Eil Malk island, Rock Islands, P...

Franco Banfi / Freshwater jellyfish (Craspedacusta sowerbii) Lake Lugano, Ticino, Switzerland. August. Invasive species.

Franco Banfi / Freshwater jellyfish (Craspedacusta sowerbii) Lake Lugano, Ticino, Switzerland. August. Invasive species.

Michele Westmorland / Snorkeler swimming with harmless Jellyfish (Mastigias papua etpisonii), Jellyfish Lake, Rock Islands, Palau, Micronesia.

Alex Hyde / Swarm of Common / Moon Jellyfish (Aurelia aurita)in sea loch, Isle of Mull, Scotland. June.

Hiroya Minakuchi / Jellyfish (Mastigias sp) group swimming, Jellyfish Lake, Palau

Michael Pitts / Jellyfish {Mastigias sp} in Jellyfish lake Palau Micronesi

Juergen Freund / Stingless jellyfish float in brackish water lake, Kalaban Is, Kalimantan, Indonesia

Remi Masson / Freshwater jellyfish (Craspedacusta sowerbii) in a lake. Rhone, Alps, France

Alex Mustard / Golden jellyfish (Mastigias sp.) in a marine lake, Jellyfish Lake, Eil Malk island, Rock Islands, Palau. Tropical north Pacific Ocean.