Alex Mustard / Leafy seadragon (Phycodurus eques). Wool Bay Jetty, Edithburgh, Yorke Peninsula, South Australia.

Doug Perrine / Pygmy shark (Euprotomicrus bispinatus) portrait, captive. Kona, Hawaii. Central Pacific Ocean.

Doug Perrine / Pygmy shark (Euprotomicrus bispinatus) portrait, captive. Kona, Hawaii. Central Pacific Ocean. Digitally manipulated image.

Alex Mustard / Great hammerhead shark (Sphyrna mokarran) female at night with Bar jacks (Caranx ruber), South Bimini, Bahamas. The Bahamas National Shark Sanctuary. Gulf Stream, West Atlantic Ocean.

Jordi Chias / Angular roughshark (Oxynotus centrina) a deepsea species living at 80-300m depth, caught by fishermen and released, Costa Brava, Catalunya, Spain, Mediterranean Sea

Claudio Contreras / Mexican blind brotula (Typhliasina pearsei) a blind cave fish, sinkhole near Tulum, Yucatan Peninsula, Mexico, August. Endangered species.

Alex Mustard / Portrait of a Severn's pygmy seahorse (Hippocampus severnsi) at Mioskon Island, Raja Ampat, West Papua, Indonesia. Dampier Strait. Tropical West Pacific Ocean.

Alex Mustard / Tasseled wobbegong shark (Eucrossorhinus dasypogon) yawning. Citrus Ridge, Yanggefo Island, Gam Island, Raja Ampat, West Papua, Indonesia.

Jordi Chias / Atolla jellyfish (Atolla wyvillei) with Gentoo penguin (Pygoscelis papua) in the background near the surface. Antarctic Peninsula. Finalist in the Underwater category of the Wildlife Photographer of t...

Solvin Zankl / Ribbon sawtail fish (Idiacanthus fasciola) from Atlantic Ocean, at a depth of 800-1000m.

Barry Bland / Fried egg jelly fish (Cotylorhiza tuberculata) Mediterranean Sea.

Alex Mustard / Reticulate stargazer (Uranoscopus sp.) emerging from the sand. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.