Xanthidium armatum ‘inverted’

The use of an inverted microscope for observation of phytoplankton, actually belongs to the standard. The image which is shown here, has been taken with the Motic Inverted Microscope AE31E. A 35 mm cell culture petri dish with a high precision glass bottom was used. This combination has some advantages over the use of an upright microscope:

• A big sample quantity of some milliliters can be investigated in a single operation, which saves quite some time.

• Desmids can be presented in a ‘not squeezed’ form. The cover glass normally used under an upright microscope, can cause loss of detail because of squeezing.

• The use of petri dishes with a high precision glass bottom, enables the use of high quality objectives (even oil immersion) with high N.A.’s, their small working distance not being an obstacle then.

• When working according to the Utermöhl method, cells sink to the bottom of the dish. The distance from the objective to the desmid is minimal, so that the theoretically achievable image quality can be approached.

Xanthidium armatum is a conspicuous desmid that is readily to be recognized. In frontal view, semicells are about octangular in outline and marked by stout, bi-or trifurcate spines on the angles. The semicell center is somewhat inflated and furnished with a corona of simple or bifurcate teeth. In the Netherlands, X. armatum is confined to oligotrophic habitats where there is a slight input of minerals from the subsoil. As a consequence of the highly acidified precipitation in the last century its occurrence is much decreased. Today it is a rare species.

Source of the last paragraph: www.desmids.nl