Normal is relative: a look at Earth’s nudibranchs

Hello, friends. I’m here today to talk to you about the genus Nudibranchia.

Yes, the nudibranchs. Often called sea slugs, although that’s not technically accurate (apparently, “snail without a shell” is not synonymous with “slug”). This is a widely varied group of creatures, with over 3 000 known species. And most of them are pretty crazy-looking. I mean, just look at these things:

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All these pictures are from a National Geographic photo gallery, click any image to go check it out.

The vivid looks are usually for either camofluage — for blending into colourful corals and anemones — or for warning predators that nudibranchs are not delicious. Which is pretty normal for Earth life, actually. But nudibranchs still look strikingly out-of-this-world. I’ve seen SFF enthusiasts using unaltered pictures of nudibranchs to represent aquatic dragons, or extraterrestrial life.

Which is why I’m talking about nudibranchs today. Because of how bizarre they look to us. It’s easy to think of Earth life as some homogenous group of “normal-looking” animals with legs and eyes and certain proportions. Humans and other primates, our pet dogs and cats, our poultry and hoofed herbivores in the barnyard. Maybe some songbirds and pest insects. Then you look at the creatures crawling around on the ocean bottom and you’re stuck with the fact that, wow. That comes from the same planet as us. We follow the same set of rules.

They say that the human race knows less about the ocean floor than we do about outer space. Which is probably why some aquatic creatures seem like they’re straight out of speculative fiction. I mean, some nudibranchs eat corals and other lifeforms that contain stinging cells. Those cells pass harmlessly through the nudibranch’s digestive system and collect in its appendages, giving the nudibranch the ability to sting. Nudibranchs steal the biological weapons of other animals. That’s a skill we associate with fantasy shapeshifters and nightmarish aliens — but these little marine snails do it all the time.

And that’s going on right now, on our carbon-based planet. In the crevices we just don’t notice while we’re doing normal human stuff. Now there’s food for thought.


3 Comments on “Normal is relative: a look at Earth’s nudibranchs”

  1. mqallen says:

    I love nudibranchs! There’s even a few delicate ones you can find where I live, in the Oregon tide pools.

  2. […] are neat! But adorabilis is also an interesting contrast to otherworldly-looking oceanic creatures, like nudibranchs and anglerfish. The sheer variety of life on our Earth should never be […]


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