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Uploaded:2020-10-13
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These fun looking sea slugs have a few unique features, not the least of which is the fact that they defend themselves by smelling like watermelon candies.

Hosted by: Michael Aranda

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Sources:
https://doi.org/10.1098/rstb.1989.0042
https://doi.org/10.1080/10236249209378807
https://doi.org/10.1111/nph.14178
https://doi.org/10.1007/PL00012669
https://doi.org/10.1007/BF01633100
https://www.montereybayaquarium.org/animals/animals-a-to-z/melibe
https://www.centralcoastbiodiversity.org/hooded-nudibranch-bull-melibe-leonina.html

Images:
https://vimeo.com/115747242
https://commons.wikimedia.org/wiki/File:Melibe_leonina_feeding.jpg
https://commons.wikimedia.org/wiki/File:Melibe_leonina_at_Monterey_Bay_Aquarium_in_2016.jpg
https://commons.wikimedia.org/wiki/File:Melibe_leonina_from_Santa_Cruz,_California.jpg
https://commons.wikimedia.org/wiki/File:Doriopsilla_BEP_7795.jpg
https://commons.wikimedia.org/wiki/File:Melibe_leonina,_Big_Sur_2.jpg
https://www.istockphoto.com/photo/whole-and-sliced-ginger-gm174822165-22729003
https://www.istockphoto.com/photo/green-forest-gm1173733640-326122715
[♩INTRO].

The lion’s mane nudibranch may not  have the charisma of an actual lion, but their method of hunting  is much more terrifying. In fact, it sets them apart  from all other sea slugs.

But it’s not their weirdest feature. No, that would be a trait you’d  never expect in an animal, and especially not one that lives in the ocean. Before we get to that, though, let’s  talk about that goofy “oral hood”.

You know, the big frilly part of their heads? That’s where they get the lion moniker, as well as the much less-fun  common name: hooded sea slug. That hood is totally unique to these slugs.

And while it might look kind of awkward, it’s actually a somewhat  horrifying way of capturing prey. See, they use them to ambush their meals things like jellyfish, little  planktonic critters, or even small fish. They just wrap it around their  prey, using those hairy edges, which are called cirri, to seal the trap shut.

The unfortunate victim is then digested  alive, because unlike other slugs, they don’t have any hard  bits for chewing or crushing. So, we should be glad they top out at about  seventeen and a half centimeters long. But, like I said, this disturbing hunting  style is not their weirdest feature.

Oh, and it’s not those paddle-like bits, either. Those are called cerata, and yes, they’re weird especially since slugs can  just discard them at will when they need to escape a predator,  a phenomenon called autotomy. But even those paddles  aren’t their weirdest trait.

What makes hooded sea slugs unbelievably  bizarre is the watermelon smell. Yes, much like a Jolly  Rancher or a scented candle, these sea slugs have a fruity, watermelon scent. YouTube hasn’t figured out Smell-o-Vision, so you’ll have to trust me on this:  They, for real, emit a melon-y odor.

And that’s thanks to a terpenoid. Even if you don’t know the word “terpenoid,” you’re probably fond of many of these  smelly, usually plant-derived chemicals. They’re what give ginger that gingery flavor, and why pine trees have that  wonderful, wintery smell.

And one—called melon heptanal,  melonal, or 2,6-dimethyl-5-heptanal, if you want to be technical,  is distinctively melon-y. In fact, we use a synthetic  version of this exact chemical in artificial melon flavors and scents. And lion’s mane nudibranchs can  emit it to deter their enemies.

Apparently, undersea predators like sea stars just aren’t as into melon-scented stuff as we are. Now, using terpenoids defensively is  something other nudibranchs do, too. But they usually get their noxious  substances from the things they eat.

Hooded sea slugs can’t really do  that, since as far as we know, none of the slugs’ prey produce melonal. And last I checked, they don’t have an assortment of fake watermelon candies to snack on, either. So, they make it themselves in  special repugnatorial glands.

Then, since their predators  flee from the fruity scent, the slugs can feel safe scooting about  and wrapping those adorable oral hoods around little invertebrates to digest them alive. Ah, the beauty of nature. Before I go, let me give a quick shout  out to our SciShow patron community!

Thanks for the nerdy discussions on discord  and, of course, your continued support! The team here wouldn’t be able to  make this show if it weren’t for you. If you’re not a patron but want to  learn more about our patron community, you’ll want to head on over to Patreon.com/SciShow And if you want to get a new,  science-packed episode of SciShow delivered to your YouTube feed every day,  be sure to click that subscribe button. [♩OUTRO].