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

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.

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

Stephane Granzotto / Freshwater jellyfish (Craspedacusta sowerbii) Angers, France.

Stephane Granzotto / Freshwater jellyfish (Craspedacusta sowerbii) Angers, France.

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.

Ingo Arndt / Diver working underwater amongst mass of Mastigias jellyfish (Mastigias sp) in Jellyfish lake, Palau, Western Pacific Islands, Micronesia, March 2009

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

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