Once I happened to exchange e-mail with Dr. Eberhard Hegewald, a specialist in Scenedesmus classification living in England. Subsequently I bought his text book and found pictures of various kinds of Scenedesmus and their related species. The overwhelming data and illustrations make it difficult to determine the exact species of this organism, but generally speaking it must be S. quadricauda.
Here we see two algal colonies, each composed of four light green cells shaped like pea pods. Each individual cell has one green protoplast in the center.
Commentary by Prof. Yuji Tsukii, Hosei University This organism is called Scenedesmus acutus f.costulatus. It is characterized by having either 4 or 8 spindle-shaped (long, tapered)cells which are arranged in rows.
A large aggregate in the center of this view is composed of bacteria, algal colonies, organic debris and mineral particles. Diatoms of various sizes go in and out of the particle, although it is not clear why they are doing so.
Commentary by Prof. Yuji Tsukii, Hosei University The diatoms in this video are too small for us to see their surface pattern, which is an important criterion for their identification.
We can also see Scenedesmus acutus, a type of green algae, in the upper left corner.
A round cell on the right may be the cystic form of a flagellate or a type of Chlamydomonas. Chlamydomonas and related organisms often attach themselves to the surface of a slide or its cover glass using their flagella, and remain still. When viewed from above, they appear round. Since we cannot see any flagella in this video, we cannot be sure if it is the cyst a flagellate or the cell of a Chlamydomonas.