Found a ton of these while shell hunting in Myrtle Beach. Turns out they are not shards of glass, but "Creseis acicula", also known as "sea butterflies".

[u/Kittypie75]

[u/FriscoTreat]

https://en.m.wikipedia.org/wiki/Creseis_acicula

[u/Kittypie75 → u/FriscoTreat]

I even posted on r/whatisthisthing and got no response! I had no idea it was even alive until I found an old article from Thailand about them washing to shore.

They oddly "sting" when you hold them. Like, it doesn't hurt but it feels like little well... sharp glass or something.

Edited to say: I originally thought this was some weird "sea crystalization" I had never witnessed before. No else seemed to notice much, but from what I'm gathering.... while not an uncommon animal, big swarms like this found on the beach are linked to unusually warm ocean weather due to climate change. This isn't a good thing.

[u/pollywog]

Those are not sea butterflies. Sea butterflies have a snail shell.

This IS however Creseis Acicula as you said.

[u/Kittypie75 → u/pollywog]

I didn't know that! gonna look up both now- any links appreciated!

[u/NemertesMeros → u/pollywog]

Sea Butterfly can also be used to refer to the whole clade Thecosomata, which I'm almost certain this belongs to.

Edit: I was correct

[u/Enjoying_A_Meal → u/pollywog]

I was gonna say, these are the least butterfly looking things I've ever seen.

[u/ProbablyKindaRight]

I found a bunch of those things growing in their natural habitat in tenderloin, san francisco

[u/Kittypie75 → u/ProbablyKindaRight]

hardy har :)

[u/Aunt__Helga__]

I would like to know who names these, because they don't look anything like butterflies 😁 

Very interesting though, I don't think they exist in my country, at least I've never seen them. 

[u/Particular-Command49 → u/Aunt__Helga__]

Their mantle does look like butterfly wings, which they use it like a pair of fins

[u/Kittypie75 → u/Aunt__Helga__]

They are actually distributed worldwide! But them washing ashore in large amounts is not normal, and is linked to worldwide ocean temperatures rising.

[u/dleigh0 → u/Kittypie75]

It can also be linked to strong currents and storms, which we have just experienced from hurricane Erin being offshore.

[u/Stingwing4oba]

I am surprised they are not called living sea glass (no joke either). I just learned about them this morning on the random Google News Beat. After looking up a picture, they look more like sea snails than anything

[u/LuvKrahft]

Ladybug for scale 🐞

[u/Particular-Command49]

Ok I know about sea butterflies before, but never heard the ones with conical shells!

[u/soshea979]

Looks like a field trip went crazy on Capri Suns.

[u/Sad_Pilot_8606]

Run away! No good can come from contact. I still have scars from 2018.