Overview

Brief Summary

Taxonomy

Diatom morphology
Diatom cells are described in two views – valve and girdle view.Cells of A. pellucida are narrowly rectangular in girdle view, and needle-shaped in valve view.They are 80--140µm long (0.08--0.14mm), 7--9µm wide in valve view, and about 6µm wide in girdle viewGirdle width varies with the stage of the cell cycle.The raphe slits are relatively short, 15--20µm long, near the ends of the valves. Each slit is flanked by longitudinal ribs that connect to a narrow rib that extends through the centre of the valve.There are parallel rows of pores crossing the valve surface – 37--40 rows in 10µm - and the pores in the rows are about 40 in 10µm.The girdle region is formed of several open bands that also contain pores.

Diatom ultrastructure
More detail of the diatom wall structure can be seen when an electron microscope is used.External views show the short raphe slits, situated towards the valve apices. The regular pores have slit-like external openings.Internal views of the valves show the ribs surrounding the short raphe slits, with a long narrow rib through the centre of the valve.The pores are more rounded and have an occlusion which is even more finely perforated - the sub-pores are so small they can only be resolved with transmission electron microscopy.
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Introduction

Amphipleura pellucida is a delicate diatom that occurs in the plankton, or at the edge of freshwater lakes.Amphipleura pellucida was first described in 1833 by Friedrich Kützing, from among some cyanobacteria (Oscillatorien) in standing water near Weisenfels in Germany. Although Kützing could see very little detail, he noticed that the diatoms could move.The diatom cells are narrow for their length, with very regular small pores.It is these small pores that made Amphipleura pellucida a favourite test object for microscope lenses - the pores are one of the smallest things that can be seen using a light microscope - they are at the limit of the light microscope’s resolution.
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Comprehensive Description

Biology

Like many diatoms, Amphipleura cells are able to glide over surfaces, but they are easily brought into suspension, and their needle-like shape allows them to remain suspended in the plankton.Diatoms have cell walls made of silica, constructed like pill- or date-boxes. They can be preserved in sediments over many centuries. The structure of the walls can be seen after cells have been treated to remove the organic contents.Species are usually identified based on the shape and patterns of the silica walls. Amphipleura is distinguished by having two short slits, one at each end of the valve (half wall), flanked by ribs, with a long central connecting rib.The fineness and regularity of the pores over the valves require very good light microscopes to be resolved.Testing the resolution of microscope lensesThe rows of pores (striae) in A. pellucida are very fine and regular - 40-42 in 10µm, with pores that are about 0.2µm apart (about 50 in 10µm).They were used to test the resolution of microscope lenses:
  • a x100 objective with a x10 eyepiece and oblique light should resolve the striae
  • a x100 objective with a x20 or x25 eyepiece with a green filter should resolve the pores within the striae
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Distribution

Distribution habitat

Amphipleura pellucida has been recorded from freshwaters in many different parts of the world.
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