Alex Mustard / Neustonic jellyfish (Porpita pacifica) at the surface, viewed from above. Anilao, Batangas, Luzon, Philippines. Verde Island Passages, Tropical West Pacific Ocean.

Claudio Contreras / Staghorn hermit crab (Manucomplanus varians) and Staghorned Hydrocoral (Janaria mirabilis), mutualist species, Angel de la Guarda Island Protected Area, Gulf of California (Sea of Cortez), Mexico, Jul...

Alex Hyde / Green hydra (Hydra viridissima) found in a garden pond. Derbyshire, UK. September. Winner of the Hidden Britain Category of the British Wildlife Photographer of the Year Awards (BWPA) Competition 2017...

Alex Mustard / Vibrant Red Sea reef scene, with orange female Scalefin anthias (Pseudanthias squamipinnis) swarming in front of Fire coral (Millepora dichotoma) feeding on plankton brought to the reef by currents. R...

Alex Mustard / Lyretail anthias (Pseudanthias squamipinnis) swimming out of protection of Fire coral (Millepora dichotoma). The Alternatives, Ras Mohammed Marine Park, Sinai, Egypt. Red Sea.

Solvin Zankl / By-the-wind sailor (Velella velella) colony, Sargasso Sea, Bermuda.

Solvin Zankl / By-the-wind sailor (Velella velella) colony from underneath Sargasso Sea, Bermuda.

Jean E. Roche / Mass of By-the-wind sailor (Velella velella) jellyfish washed up on beach, Camargue, France, May.

Jean E. Roche / Mass of By-the-wind sailor (Velella velella) jellyfish washed up on beach, Camargue, France, May.

Jean E. Roche / Mass of By-the-wind sailor (Velella velella) jellyfish washed up on beach, Camargue, France, May.

Pascal Kobeh / Diver near pink coral (Distichopora violacea), Maldives, Indian Ocean.