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Arcella from a paddy field

After being collected from a paddy field, the sample was put on 1% agar plate with a drop of distilled water and kept in the dark for 4 days.

In the first scene of this video, a testate amoeba Arcella is moving slowly among aggregates. In the second scene, the amoeba notices a green organism that comes near. In the last scene, the Arcella has caught the green organism and is consuming it. Unfortunately, the video did not film the moment of capturing the organism.

Commentary by Prof. Yuji Tsukii, Hosei University
This large amoeba with a disk-shaped shell (test) and thick pseudopodia is a testate amoeba called Arcella.

As the several parts of its comparatively high shell appear depressed, the organism is most likely Arcella gibbosa.

But, as the depression in the underside of the shell is not so clear, it might also be Arcella vulgaris.

The green organism that approaches belongs to genus Trachelomonas, because it is surrounded by a shell (lorica) and exhibits characteristic locomotion. Trachelomonas is also characterized by a red eyespot in its cytoplasm.

Newly formed shells of trachelomonas are transparent and gradually become reddish-brown. As this organism has a transparent shell, it has probably just divided.

The organism might be Trachelomonas crispa, but we cannot see the long, spiky spines surrounding the opening where the flagellum extends, which are a characteristic feature of Trachelomonas crispa.

Another possibility is that the organism belongs to genus Strombomonas. However, the opening (outlet) for the flagellum of Strombomonas is characterized by a narrower structure like a bottleneck. Therefore the organism may be Trachelomonas rather than Strombomonas.

Sampling Date : 22 September 2006

Sampling Site : KASHIMADAI paddy field  Google Map

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