Which diatoms do we see here?

The Macrofauna Werkgroep Groen Hart Leudal in The Netherlands, found some diatoms in the river Swalm near their clubhouse. It is a challenge to name diatoms if the cell contents are still present in the silica skeleton. The organic content should be removed first with the help of chemicals. Yet an attempt can be made to identify these still living tiny algae, which were caught on video with the help of the Motic inverted microscope AE31E with Motic PlanApo 20X and 40X objectives and the Moticam cameras 1080 and S6.

The Swalm is a small river in Germany and the Netherlands. Its source is in North Rhine-Westphalia, Germany. The Swalm flows into the Meuse across the border with the Netherlands. Its total length is 45 km.

The wetland overgrown with trees and heath/bog areas along the Swalm provide a diverse habitat for fauna and flora. Frogs, dragonflies, damselflies, blue throat, kingfisher and golden oriole are to be found as are water crowfoot, bog myrtle and other rare plants. Brown trout, barbel and chub are at home in the river; along the river banks are also various members of the beaver rat family.

Which diatoms do we see in the video?

Panthera UC-Plan and diatoms

Diatom skeletons that are free of their content like chlorophyll etc. are excellent objects to test and compare the quality of microscope lenses. In this case, some pictures of the recently marketed Motic Panthera are shown.

The photos are stacked to show the sharpness over the entire length of the diatom. The actual microscopic images through the Panthera microscope are even sharper. Some sharpness is lost by the camera and the photo stacking program.

Diatoms - Jewels of the Sea

Diatoms are unicellular algae that are found wherever there is water and sufficient light to stimulate photosynthesis. The cells may be free floating (planktonic) or attached to a substratum (sessile). The diatom cell possesses the property of being able to surround itself with a more or less rigid box-like (like a covered petri dish) skeleton of hydrated silica called a frustule. The classification of diatoms is largely based on frustule form and sculpture. Diatoms range greatly in size from 5 – 2000 μm in length, although most species encountered are in the size range 20 – 200μm. 

Introduction to Darkfield illumination - Slider solution

For transparent samples in light microscopy, dark field illumination is a simple and affordable contrast method. The idea of this technique is to display and to emphasize border structures, means abrupt changes of the refractive index within the sample. Especially for single-celled organism in fresh or sweet water environments, with a refractive index close to water, this contrast method gives aesthetic and informative images.

Dark field emphasizes borders and isolated, single structures, flagella of protozoa and tiny particles. The comparison of a diatom sample in bright field and dark field clearly shows this:

How such an image is achieved? We need to eliminate the direct light which ordinarily passes the specimen and which is responsible for the bright background in bright field illumination. For objectives with a Numerical Aperture ≤ 0.65 this