Live diatom needs ID

[btschumy]

Can anyone help ID this diatom? The closest I can come up with is Sellaphora, but most diatom keys seem mainly for cleaned specimens, not living.

Diatom4.jpg (198.66 KiB) Viewed 4627 times

[hkv]

Looks very similar to this one which he claims to be "Pinnularia Viridis". BUT, I am no expert. I am sure other will chime in soon.

https://www.flickr.com/photos/bills_pho ... 5565085461

[btschumy]

It does look the same as his. Whatever it is, they are almost surely the same thing. Thanks for the link.

[charlie g]

Thanks, Bill, for your diatom encounter...yup...these freshwater 'cough drops'/ as in the Smith Brothers losengers (?sp?) I always think of when i encounter these live diatoms...these are fascinating.


I will peruse my cluttered library soon...and get back with an opine. Just my anecdotal sense of things...I sense in dead of our northern hemisphere winters...these 'cough drop diatoms' manifest so many more oil-inclusions than during the growth season...just my sense. Thanks for sharing this microscopy, Bill. charlie guevara

[KurtM]

Looks very similar to this one which he claims to be "Pinnularia Viridis". BUT, I am no expert. I am sure other will chime in soon.

https://www.flickr.com/photos/bills_pho ... 5565085461

William Mark is certainly a very experienced microscopist, and though I have no particular reason for doubt, I wonder how he diagnosed genus and especially species here. Probably observed it rotating? You're looking at a girdle view - note the classic "shoe box" arrangement of how the epivalve and hypovalve fit together at the ends. Charlie's example appears to be reproducing.

[btschumy]

Kurt,

Thanks for chiming in. I'm so dumb that I didn't realize this was a girdle (edge on) view. Not clear to me how you ID something from this view. I would think it somewhat rare to find diatoms lying exactly edge on in a wet mount.

I don't see a shoebox shape where the valves fit together in my image. Is there supposed to be a midline running the length where the top and bottom valves fit together?

[charlie g]

I feel your pain, Bill...so much to learn...and these are not beetles..now there is structure and intricacies within structure and intricasies!

As Kurt openned yours and my eyes to orientation of what we are looking at ( again thanks Kurt for all your shared microscopy). Girdle view need not be thought of like balancing a plastic bank card on it's edge...girdle orientation is often a very wide surface. Looking down at a diatom from above..it's valve-view may be a shape with pointed poles. Looking at same diatom frustule ( the silica case the diatom made) in 'side view'/ girdle view..the diatom can be rectangular in shape!

Excellent online resources for diatom morphology terms...these cough-drop diatoms reflect for me how often I encounter said creatures in their: 'girdle view'. charlie guevara

[Charles]

Your diatom does appear to be a Pinnularia in girdle view. The pinnularia size in girdle view is about the same size in valve view so they can be commonly seen in both views. Attached is one of my photos of cleaned Pinnularia taken with a B&L stereo scope which shows both a girdle view and valve view on the far left.

1Pinnularia.jpg (152.52 KiB) Viewed 4565 times

[KurtM]

Kurt,

Thanks for chiming in. I'm so dumb that I didn't realize this was a girdle (edge on) view. Not clear to me how you ID something from this view. I would think it somewhat rare to find diatoms lying exactly edge on in a wet mount.

I don't see a shoebox shape where the valves fit together in my image. Is there supposed to be a midline running the length where the top and bottom valves fit together?

Even folks who study diatoms sometimes get caught by a strange frustule that turns out to be a girdle view of a familiar type! It's just one of the finer points you learn to be on your toes for.

Living diatoms often exhibit lively movement, and rolling about their long axis like a rotisserie is nothing unusual. When they do, then you get alternating valve and girdle views.

Diatoms are built quite a lot like Petri dishes. The flat dish faces represent the valves, and the rims the turned-down edge, called the mantle. The top and bottom overlap just as the top and bottom of the Petri dishes do, one fitting over the other. This overlapped edge, then, makes up the girdle. (There may also be girdle bands, which I omit for brevity, and if you want to learn more just Google diatom morphology and select Images for a quick primer.)

In the first image in this thread the overlap is clearly seen on the left. No line is seen going down the middle, probably out of the focus plane.