Algae Identification - New one on me

[coltonwsmith]

Maybe I'm ignorant, but I can't recall having seen this kind of algae. At first I thought it was diatomic of some sort, but now I'm not sure. It seems that Hermit Crabs die shortly after ingesting it.



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[54seaweed]

looks like sponge to me , I don't think the hermits are dying from it , more likely killing one another for shells

 

[mr_X]

I'm going to guess Dinoflagellates.