Cylindrical Diatom

[75RR]

Planapo 63x/1.4, DIC, 25µm diameter, marine sample, 17 image stack in Photoshop

Cylindrical diatom attached to an alga that is coated with small oval diatoms

[75RR]

Here is what looks to be a spherical one from the same session.

Planapo 63x/1.4, DIC, 30µm diameter, Marine sample, 15 image stack in Photoshop.

[gconcepcion]

Here is what looks to be a spherical one from the same session.

Planapo 63x/1.4, DIC, 30µm diameter, Marine sample, 15 image stack in Photoshop.

Great images! To be honest, the second photo of the spherical protist looks like a dinoflagellate to me. Maybe in the genus Alexandrium, or Protoceratium? Or a Gymnodinoid? Would need to see more individuals and a view of the sulcus if possible to be more confident.
I'm a little bit Rusty, but the groove around the center of the sphere looks to me like a stereotypical dinoflagellate cingulum. Did you observe movement? Was it smooth, or more "twirly"?

cingulum

[75RR]

Thanks gconcepcion

I did wonder at the time if there were any spherical diatoms, I suspect not, but did not know what else to call it.

There was no movement, which is what allowed the sequence of stackable shots

[Mintaka]

Love the first picture especially.

[75RR]

Thanks Mintaka, glad you liked it.

[gconcepcion]

There was no movement, which is what allowed the sequence of stackable shots

Right, that makes sense. If you happen to see others on the same slide, see if it's possible to get any ventral shots that show the sulcus (longitudinal groove) which would be a pretty big confirmation.



The patterning that you see is what I think to be the thecal plates. These fluoresce blue if you stain the specimen with calcofluor and can be another indication of Phylum Dinoflagellata

[actinophrys]

Spherical diatoms definitely do exist. Most form chains, as for instance in freshwater Melosira, but it looks like some also occur as single cells, like Podosira from seaweeds. Apparently auxospores can also be rounded, but I do not know much about how they look. In any case, though, I think the lovely detail in this photo – the look of the chloroplasts, hexagonally arranged punctae, and apparent flatness of the equatorial band – support it as some such diatom.

[gconcepcion]

Spherical diatoms definitely do exist. Most form chains, as for instance in freshwater Melosira, but it looks like some also occur as single cells, like Podosira from seaweeds. Apparently auxospores can also be rounded, but I do not know much about how they look. In any case, though, I think the lovely detail in this photo – the look of the chloroplasts, hexagonally arranged punctae, and apparent flatness of the equatorial band – support it as some such diatom.

I don't necessarily disagree, what I was originally were thinking as theca are certainly the plastids (brushes off some of the rust...)... but it could still be a gymnodinoid (naked/athecate) dinoflagellete or another family. The punctae patterning also makes me think diatom, however dino's also show patterning at high magnifications: Dinoflagellate high resolution