Diatomeen aus dem Nordatlantik

[Bob]

Hallo zusammen,
bei unserem Mikrotreffen am letzten Samstag haben wir uns unter anderem Plankton aus der Nordsee und aus dem Nordatlantik angesehen, wobei besonders letzteres viel interessante Diatomeen enthielt. Ich habe daher die eingetrocknete Probe von drei Objektträgern abgespült, von Alkohol und Salz befreit, durch Veraschen etwas gereinigt und in Pleurax eingeschlossen. Anbei ein Foto, das dabei herausgekommen ist. Durch das Eindeckmittel mit sehr hohem Brechungsindex wird die ganze Schönheit sichtbar gemacht.
Das Veraschen reinigt zwar nicht allzu gut, dafür bleiben Kolonien aber oft erhalten.

Falls jemand eine Identifikation beisteuern könnte würde ich mich freuen.

Das ist auch gleich ein Vorgeschmack auf unser MIKRO Hamburg-Thema im Februar, wo uns neben einem interessanten Vortrag das Herstellen von Präparaten aus fertig gereinigtem Diatomeen-Material erwartet.

Viele Grüße,

Bob

[Bob]

Und hier noch eine Kolonie, die bei der Reinigung zusammengeblieben ist.

Viele Grüße,

Bob

Nachtrag: Vermutlich Thalassionema nitzschoides

[Bob]

Und hier noch ein centrales mit interessanter Struktur.

Nachtrag: Vermutlich Thalassiosira punctigera

[Rene]

Hi Bob, your second image looks like Thalassionema nitzschoides, and your last image probably is Thalassiosira punctigera, if you took it with oil immersion  (the areolar structure should be very fine). Darkfield illumination shows all kind of artefacts in your image, and the stacking is off. Darkfield imaging and stacking are not the most suited techniques if you ask for help with identification. But your Thalassionema img certainly is a beauty!

HTH, René

[Bob]

Hi René,
thank you for the identification!
These images were taken with Zeiss DIC old in the middle position of the analyser with the interference strip running through the image. I was in a hurry and just wanted to see how good the slide has become and took the images with the Zeiss Jena Dry Apo 40 /0,95. I have to repeat it with oil immersion and a bit more time at hand. Would you suggest single image brightfield as best for identification purposes?

I took one stacked shot of an other centrales siting diagonal in the mountant. Compared to the Thalassiosira it had only two spines per side as fas as I could gather from the single images. Image quality is really lacking here as the diatom was further and further away from the cover slip due to the angle it sits in the mountant.

Bob

[Rene]

Well, that last one is a good oversight image! I would say this is Thalassiosira punctigera. the amount of bigger spines in the ring of small spines is variable.

In stacked images details disappear. Also, sometimes it is necessary to know for example whether a diatom valve is curved or flat.


Best wishes, René

[Bob]

In stacked images details disappear.

Hi René,
this was the case with one big spine here. The one in 6 o'clock position ist clearly visible, the one in 12 o'clock position was there in the single images, but got picolayed-out .
For stacking I have nothing but my feel in the finger tips and this were 60 images spread over not much height, so no stepper motor or so. Right now I'm into the preparations of a diatom slide making group meetings and have more to do with chemically cleaned material, these plancton slides just came in between as the sample appeared.

Bob