Sea angels are mind-bogglingly weird

Sea angels are surreal little beasties that look more like Pokemon than actual living creatures – proof that the ocean is far more mysterious than we give it credit for.

Contributor Bec Crew Contributor Bec Crew Becky Crew is a Sydney-based science communicator with a love for weird and wonderful animals. From strange behaviours and special adaptations to newly discovered species and the researchers who find them, her topics celebrate how alien yet relatable so many of the creatures that live amongst us can be.

By Bec Crew • Reading Time: 2 Minutes

Image credit: Aquatilis/YouTube

Found all over the world, from polar regions to tropical seas, sea angels are free-floating sea slugs with wing-like appendages called parapodia, and a gelatinous, mostly transparent body. Also known as gymnosomes, these things are absolutely tiny, with the largest species, the naked sea butterfly (Clione limacina), stretching just 5 cm long.

They might not appear all that threatening (although those horns do look more devilish than angelic), sea angels are the worst nightmares of the almost-as-wonderful sea butterflies. Sea butterflies, which also have to be seen to be believed, are tiny sea snails, and they are the preferred meal of the sea angels.

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Sea angels often get the upper hand on sea butterflies, because their ability to zoom through the ocean at 100 mm per second, means they can swim twice as fast as their prey. They’re also able to lay enormous traps of mucous webs to snare an unfortunate sea butterfly.

Close to home, sea angels have been found all along the north-east coast of Australia and up around Papua New Guinea. The stunning specimen in the image above was spotted in the icy waters of the White Sea, off the northwest coast of Russia:

Sea angels are protandrous hermaphrodites, which means they start out male and turn female throughout the course of their lives. Clownfish are a great example of this type of hermaphroditism, which makes Finding Nemo a far more complicated scenario than the movie suggests.

Protandrous hermpahrodites are the exact opposites of protogynous hermpahrodites, which start off female and end up male. This is by far the most common form of hermaphroditism seen in marine life.

When sea angels want to mate, they will draw in close to one another and turn their reproductive organs inside-out. They’ll proceed to bind themselves together using a specialised sucker, which leaves a nasty scar when they finally separate.

For up to 4 hours, the sea angel pair will float through the ocean as the fertilisation process takes place, spinning around like they’re dancing. It’s absolutely bizarre, and lucky for us, marine biologist, Alexander Semeno, has managed to film it:

And how’s this for multitasking – the pair will sometimes hunt for food while they’re mating, which sounds like a very George Costanza thing to do, if it didn’t require so much effort.