Mesostigma
Mesostigma is a genus of green algae, which is at the base of the entire group of Chloroplastida. There are two types in freshwater.
Features
The alga is unicellular with two approximately equal-length flagella. The diameter is 11 to 25 micrometers. The cells are much flattened and saddle-shaped curved. The flat is located along the longitudinal axis. The two flagella sit at the middle of the flat cell, the scourge pit is difficult to see. The basal body, or its transition region resembles that of the Streptophytina. The eye spot is pale and sits at the rear end.
The cell wall consists of cellulose. Sit on the surface and on the scourges scales of different sizes. They are up to one micron in size. You will cover the cell uniformly and completely. Each cell has a disk- shaped chloroplasts with two pyrenoids standing on the edge. In Mesostigma grande the pyrenoids are absent. The chloroplast is usually bulged at the edges and appears a ring in apical view. At photosynthetic pigments chlorophyll a and b occur. The chloroplast is surrounded by a double membrane, endoplasmic reticulum, a periplastidäres does not exist. Thickness is formed within the chloroplast. Near the scourge pit are several contractile vacuoles.
Mesostigma swims sideways under rotation. The two flagella beat it unequal.
Reproduction is by asexual cell division. Sexual reproduction is not known.
Occurrence
Mesostigma occurs in fresh water in stagnant water, usually in rather low numbers.
System
The systematic position of the genus is not entirely clear. The scourge structure is similar to the Charophyta. Phylogenetic studies based on rbcL sequences and four - gene analyzes ( rbcL, atpB, and 18S rDNA nad5 ) Mesostigma saw as a sister group of the Charophyta. Several other studies they saw as a sister group of all other Chloroplastida, so as basalste group. This view is 9' -cis- neoxanthin supported by the presence of the dye, while all other Chloroplastida trans - neoxanthin own. Anyway Mesostigma is very close to the base of the entire green algae ( Chloroplastida ).
There are two types:
- Mesostigma grande Korshikov
- Mesostigma viride Lauterborn