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Everyone's all like “wow look at how many different arthropods have turned into crabs.” Y'all, that's nothing. Here's a thread of arthropods that have gone completely off the rails. 
First: the barnacle that turned its cute little baby barnacle body into a cute little baby barnacle body+head needle that it uses to injects its insides into a crab, where those insides grow like mold & get so big ovaries burst from the crab's abdomen. https://jellybiologist.com/2018/10/31/this-may-be-the-oceans-most-horrifying-monster-and-youve-probably-never-heard-of-it/
Worms? Not worms, these are arthropods that have evolved to look like maggots and live inside mammals and snakes. This poor leopard did not see this arthropod coming.
Pic: @The_Episiarch http://bit.ly/3tipoE4
Pic: @The_Episiarch http://bit.ly/3tipoE4
Then there are the shark barnacles that grow on top of (and in the process chemically castrates) sharks. Did I mention these barnacles evolved roots that they use to sink into shark flesh?
Pics: https://bit.ly/3j9khRN
Pics: https://bit.ly/3j9khRN
Then there are the barnacles that live on dolphin teeth. Because WHY NOT?!
Pic: @shirokito https://bit.ly/36xmZvB
Pic: @shirokito https://bit.ly/36xmZvB
Snowflake? NOPE. Crab that lives inside a sea star. https://twitter.com/manpokenautilus/status/1337622524809527296
Oh, and we haven't even got to these guys. Their free-living cousins look like little shrimp, but these copepods live instead on THE EYES OF GREENLAND SHARKS. Because who wouldn't want to be shaped like a tube stuck on the cornea of a 400-year-old predator??
[pic=wiki]
![Oh, and we haven't even got to these guys. Their free-living cousins look like little shrimp, but these copepods live instead on THE EYES OF GREENLAND SHARKS. Because who wouldn't want to be shaped like a tube stuck on the cornea of a 400-year-old predator?? [pic=wiki]](https://pbs.twimg.com/media/EtMSiWAWQAc_6s2.jpg "Oh, and we haven't even got to these guys. Their free-living cousins look like little shrimp, but these copepods live instead on THE EYES OF GREENLAND SHARKS. Because who wouldn't want to be shaped like a tube stuck on the cornea of a 400-year-old predator?? [pic=wiki]")
[pic=wiki]
You know those white patches on whales? Did you know they're ALL WHALE LICE? https://twitter.com/jkfordays/status/1321902328098648065
In conclusion: arthropods know no bounds, can literally become anything, and we should all be awed and afraid. [end of thread]
(p.s. here are some lumpfish to remind you the ocean can still be good.) https://twitter.com/RebeccaRHelm/status/1310580499862163457
also i kinda scared myself with this thread and now i don't want to go to bed... 
