I wanted to post about these, and some of the things that persuade me it's not Dinos, and indeed is chrysophytes.
The best matches in phycokey I've seen are 3 chrysophytes in the group non-flagellate colonies.
*
Chysocapsa
*
Tetrasporopsis
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Chysosaccus
These are very good visual matches (size, shape, color, cell structure, organization) for the best microscope shots I've seen from a couple of different users.
additionally, the descriptions are spot on for what reefers have described.
"Amorphous colonies with unpigmented gelatinous extracellular matrix." "Colony with cells embedded in mucilage, in groups of four." "Gelatinous colonies of non-flagellated globose cells."
The thing troubling me was that
ALL of these are freshwater.
Running across that paper
@mcarroll talked about with the benthic chrysophyte growths in Corsica made me feel much better that there are indeed relatives of these guys that match the traits and show up in marine habitats. And benthic too. Fits very well.
Furthermore: there's another fantastic paper (brand new) that tries to disentangle the classification issues within these related groups of marine chrysophytes.
A Re-investigation of Sarcinochrysis marina (Sarcinochrysidales, Pelagophyceae) from its Type Locality and the Descriptions of Arachnochrysis, Pelagospilus, Sargassococcus and Sungminbooa genera nov.
(I'll be honest, I don't care much about classification within sub-orders of chrysophyte - I read it for the pictures)
One thing I'd like to see done - just as a demonstration:
Get a sample of these golden chrysophyte guys under the scope, and add a drop of zooxanthellae harvested from a coral (softies are easy). Try to get cells of each in the same microscope shot. What I expect we'll see is that the colors are definitively different - the symbiotic dino from the corals should look a good bit more brown, and these chrysophytes more golden.