Diatoms from Puget Sound

Charles Krebs · Post by **Charles Krebs** » Sat Feb 18, 2012 1:59 am

Here are a few diatoms from my latest "catch". These centric diatoms were the most common. On one slide I had a few on their "side" so I was able to get shots looking into the girdle. The second image is a single shot showing this side view, and is included as a set-up for the third shot (so you have some reference as to what you are looking at!). I found the third image interesting because it clearly showed something I had never seen before. This "optical section" shows structures inside the diatom at the center of the disk. Anyone know anything about these features? (This third shot also gives an interesting glimpse at the overlapping thecae).

The last image is a star shaped diatom frustule, the only one I found in this batch, and one I don't see too often.

RogelioMoreno · Post by **RogelioMoreno** » Sat Feb 18, 2012 2:48 am

Charles,

Beautiful set, the last one is amazing!

Rogelio

Jean-marc · Post by **Jean-marc** » Sat Feb 18, 2012 3:26 am

Hi Charles,

The third one is very interesting.
beautiful set.

Best

JM

René · Post by **René** » Sat Feb 18, 2012 6:27 am

Hi Charlie, nice set again! Based on what we come across in european waters I would say it is either Coscinodiscus centralis or C. pavillardii. The latter one would show a dimple in the centre of the valve, but that is hard to make out on your stacks. C. centralis would show typical internal structure within the areolae, but it would need oil immersion to show it clearly.

What you see within the diatom is a large space full of water, the vacuole, which in fact makes out most of the diatom volume. The cytoplasm (with the chloroplasts) lines the wall of the frustules and a nucleus is located at the wall in the centre of one of the valves. A couple of strands of cytoplasm are spreading out from the nuclear region to the other side of the frustule. It is pretty common arrangement. In some diatoms (eg Lauderia), the nucleus is split in two on either side, with a thin plasma strand connecting them. I think Franz Neidl showed it in earlier images.

The last diatom looks like Triceratium reticulum

Best wishes, René

Charles Krebs · Post by **Charles Krebs** » Sat Feb 18, 2012 12:39 pm

Thanks all!

René,
Thanks for the detailed description of what is seen "inside".

Any "dimple" in the valve center is very slight. I realize for a definitive ID you probably need to see details not shown here, but would these be possibilities as well...

Coscinodiscus radiatus
Triceratium pentacrinus

Cactusdave · Post by **Cactusdave** » Sat Feb 18, 2012 1:31 pm

Lovely images, really crisp and detail-filled. Should the title be 'Diatoms from Puget Sound' BTW?

Charles Krebs · Post by **Charles Krebs** » Sat Feb 18, 2012 1:43 pm

Dave,

Should the title be 'Diatoms from Puget Sound' BTW?

Yup... and I just corrected that.
... must have been the 12:59am posting time...

René · Post by **René** » Sat Feb 18, 2012 3:40 pm

Hi Charlie, C. radiatus is flat, really flat and thin as a coin.
For C pavillardy, the upper focal point would clearly first show a ring of areolae, when going down then the central area would get into focus. There's a hint of the areolar structure in your lowest image visible (just above the central area of the valve), would that be with the 40x objective?
I think it is save to assume you have C centralis here.

T. pentacrinus always show lines on the (inner) surface, not sure of the terminology there. Anyway, no sign of them in your image. Also the pore fields in the star points is different from pentacrinus.

Best wishes, René

that image with the golden sphere is breathtaking btw. precision enginering from a biological machine!