Today is International Day for Biological Diversity. An opportunity to celebrate and wonder at the amazingly diverse variety of species we share the planet with. This year it has a water theme, so we’ve been having some fun over on Twitter, and here’s our pick of the weirdest and most wondrous watery wildlife you definitely need to know about. 1. ClownfishIt’s the untold story of Finding Nemo that clownfish change gender. When the dominant female in a group is removed, a male steps up to take charge. So in the film, Nemo’s dad should have had a more dramatic storyline! 2. Pink dolphinsAmazonian river dolphins are pink. But they don’t know that because they are blind. There’s not a lot of point being able to see when you live in murky water and echo-locate 3. Arctic wormWorms that live in the ice and turn to goo when the temperature gets above freezing point. Who needs science fiction? 4. Spirit bear The black bears that live in the Great Bear Rainforest are unusually coloured. Some are almost polar bear-white. These spirit bears gorge on salmon which brings nutrients all the way from the sea, up the river, into the forest, and fertilise the trees. 5. Narwhal Turns out that that wacky tusk on these Arctic whales isn’t just for show: it’s a super-sized super-sensory organ. Make your own jokes... 6. Barnacles Barnacles are stuck. They don’t get out much. So they have exceptionally long penises to reach other barnacles, so they can, you know, make baby barnacles. 7. Arctic tern The only wild bird to be recorded on all the world’s continents, the Arctic tern migrates from the Arctic to the Antarctic to get two summers every year. 8. Mimic octopus Is it a bird, is it a plane? Chances are it could be a mimic octopus. Changing shape, colour, size and movement to pretend to be all sorts of ocean critters. As if being an octopus wasn’t awesome enough already? 9. Immortal jellyfishThe never-ending story of this gelatinous wonder is that it doesn’t have to die. Able to convert back into larvae this jellyfish is immortal. In the right conditions, they may take over the world. Don’t say I didn’t warn you. 10. Shrew portaloo Perhaps the most awesome evolutionary solution in nature – the shrew whose loo is a carnivorous pitcher plant. As if it weren’t already amazing, the pitcher plant has evolved to devour the poo. Everyone’s a winner. (The shrew loo made it through as ‘watery’ because of the plumbing element.)