Marine biologist, underwater photographer and head of the divers’ team at Moscow State University’s White Sea Biological Station, Alexander Semenov, has captured thousands of creatures in the deep sea, and most of us are unlikely to ever see and experience them ourselves in their natural habitat. Fortunately, Semenov generously shares his knowledge, experiences and his amazing photographs and videos of the creatures in the deep with the human land-dwellers of the world.

One such creature he discovered hovering under the ice in the White Sea, off the northwest coast of Russia is a Sea Angel. Apart from two tiny horns at the top of its body, the name is quite apt for the tiny, translucent creature, flapping its wings while moving through the water in slow motion. It seems surreal, floating in the dark, like an alien in an animated science fiction movie. Indeed, the little sea angel and thousands of others living in their water universe are alien to most of us.

Sea angels (clade Gymnosomata) are a large group of extremely small, free-floating sea slugs with a jelly like transparent body and wing-like attachments called parapodia. They are found from the polar regions to the tropics grow bigger in colder water compared to those in the tropics. The naked sea butterfly (Clione limacina) is the largest species and reaches 5cm in length. They have terminal mouths with the radula common to mollusks, and tentacles to grasp their prey, sometimes with suckers similar to cephalopods. Their ‘wings’ allow them to swim at speeds up to 100 mm/s (0.22 mph), about twice the speed of the sea butterfly, their preferred prey.

The angels are simultaneous hermaphrodites, meaning they have complete or partial reproductive organs and produce gametes normally associated with both male and female sexes. Fertilization occurs internally. When they’re ready to mate, they’ll get close together and turn their reproductive organs inside-out, then attach to each other with a specialised sucker. During the fertilisation process, the pair will float and spin together in a slow motion dance for up to four hours, even enjoying a meal together while they’re at it. After fertilization they spawn a gelatinous egg mass which will float freely until they hatch. The embryonic shells are shed within the first few days, and a new generation is born.

According to Semenov, only about 236,000 species of marine organisms have been discovered over the last 2000 years. Scientists estimate that to be only 8-10% of the total creatures living in our oceans, leaving about 2-3 million species yet to be discovered.

Semenov’s passion for our oceans and the creatures who made it their home is obvious. On his website, coldwater.science, he wrote:

‘’The World Ocean is as close as you can get to outer space without leaving Earth. It’s an entirely different universe, nothing like the life we have on land. And while people dream about alien life forms from other planets, there is another universe right here, closer than anyone expects. As a marine biologist and underwater photographer, I have been studying and documenting this world for more than 10 years, organizing expeditions to the far-off corners of the planet, spending days and weeks under the polar ice, giving lectures, teaching classes at schools, writing books and making movies with a whole team of great people involved in my own project «Aquatilis».’’

» Source