Desmidiales

Micrasterias (mike-ras-tear-ee-ass), iconic desmid. The desmids are one type of green algae, often associated with slightly acidic freshwater habitats. As with most desmids, they are formed from two mirror imaged cells. Cellulosic wall, plastid, and pyrenoids are evident. The nucleus is in the centre. Phase contrast.

Micrasterias is one of the desmids, flattened green algae in which the organism has a central constriction which gives the organism the appearance of being two cells joined together. This detail showing the central nucleus. Differential interference contrast.

Differential interference contrast.

Differential interference contrast.

Staurastrum (star-ass-strum) desmid - a green alga with (as is usual for green algae) a cellulose cell wall which has a star-shaped appearance, and bright green chloroplasts. Differential interference contrast.

Filemaoentous desmids, cells located within a thick mucus sheath. A green alga, with cellulosic cell walls and bright green chloroplasts. Two forms are shown here. Phase contrast micrograph.

FIlaments (unhappy) observed in freshwater sediments in the vicinity of Broome, Western Australia in September 2003. This image was taken using differential interference contrast optics. Â Â This work was supported by the Australian Biological Resources Study.

This image of filamentous desmids shows the mucus layer in which the cells are embedded.

Cosmarium (cos-may-ree-um) caelatum. Cosmarium is a very common and large genus of alga found usually in oligotrophic, acid waters. The cells of this genus are composed of two semi-cells, constricted in the middle. This region is termed the isthmus and is where the nucleus is found. The outer portions of each semi-cell contain a single, large chloroplast. The outer cell wall of each semi-cell is covered with pores and can be very ornate with the pattern being useful in distinguishing among species. The cells move slowly using mucilage secretion to create the force for movement. Both asexual and sexual reproduction occurs. The asexual reproduction is by cell division and the sexual reproduction involves the formation of zygospores. The gametes migrate from the parental cells, passing through pores to fuse in a region midway between the parental walls. The zygote can form a very ornate wall. This specimen was collected in a moor located in the Salzburger Land, Austria. This image emphasizes the ornate cell wall of Cosmarium ornatum. This specimen measures 49 microns long and 38 microns wide.

Cosmarium (cos-may-ree-um) caelatum. Cosmarium is a very common and large genus of alga found usually in oligotrophic, acid waters. The cells of this genus are composed of two semi-cells, constricted in the middle. This region is termed the isthmus and is where the nucleus is found. The outer portions of each semi-cell contain a single, large chloroplast. The outer cell wall of each semi-cell is covered with pores and can be very ornate with the pattern being useful in distinguishing among species. The cells move slowly using mucilage secretion to create the force for movement. Both asexual and sexual reproduction occurs. The asexual reproduction is by cell division and the sexual reproduction involves the formation of zygospores. The gametes migrate from the parental cells, passing through pores to fuse in a region midway between the parental walls. The zygote can form a very ornate wall. This specimen is 49 microns long and 38 microns wide.

Cosmarium (cos-may-ree-um) praegrande. Cosmarium is a very common and large genus of alga found usually in oligotrophic, acid waters. The cells of this genus are composed of two semi-cells, constricted in the middle. This region is termed the isthmus and is where the nucleus is found. The outer portions of each semi-cell contain a single, large chloroplast. The outer cell wall of each semi-cell is covered with pores and can be very ornate with the pattern being useful in distinguishing among species. The cells move slowly using mucilage secretion to create the force for movement. Both asexual and sexual reproduction occurs. The asexual reproduction is by cell division and the sexual reproduction involves the formation of zygospores. The gametes migrate from the parental cells, passing through pores to fuse in a region midway between the parental walls. The zygote can form a very ornate wall. This specimen was collected in a moor located in the Salzburger Land, Austria. The semi-cells of Cosmarium praegrande are spheroid and the cell walls are densely covered with conical granules except for a small area at the apex. This specimen is 40 microns long - smaller than those described in the literature (88 - 122 microns).

Cosmarium praegrande P. LUNDELL  The cells are up to 1.7 times longer than wide. The cell halves are spherical. The central cuts are deep and narrowly rounded on the inside and extend strongly towards the outside. The cell wall is covered with conical verrucae. They are arrranged in transverse rows which are shifted against each other. Between the transverse rows there are fine pores. The vertex view is circular in shape.  Length 95 - 100 µm, width 55 - 65 µm. Occurrence: Rare occurrence in Central Europe in fens and quaking bogs.  

Cosmarium (cos-may-ree-um) pseudoornatum. Cosmarium is a very common and large genus of alga found usually in oligotrophic, acid waters. The cells of this genus are composed of two semi-cells, constricted in the middle. This region is termed the isthmus and is where the nucleus is found. The outer portions of each semi-cell contain a single, large chloroplast. The outer cell wall of each semi-cell is covered with pores and can be very ornate with the pattern being useful in distinguishing among species. The cells move slowly using mucilage secretion to create the force for movement. Both asexual and sexual reproduction occurs. The asexual reproduction is by cell division and the sexual reproduction involves the formation of zygospores. The gametes migrate from the parental cells, passing through pores to fuse in a region midway between the parental walls. The zygote can form a very ornate wall. The semi-cells of Cosmarium pseudoornatum are covered with more or less circularly arranged granules. The chloroplasts have two pyrenoids per semi-cell. This specimen was collected in a moor located in the Salzburger Land, Austria. Differential interference contrast.

Cosmarium (cos-may-ree-um) venustum. Cosmarium is a very common and large genus of alga found usually in oligotrophic, acid waters. The cells of this genus are composed of two semi-cells, constricted in the middle. This region is termed the isthmus and is where the nucleus is found. The outer portions of each semi-cell contain a single, large chloroplast. The outer cell wall of each semi-cell is covered with pores and can be very ornate with the pattern being useful in distinguishing among species. The cells move slowly using mucilage secretion to create the force for movement. Both asexual and sexual reproduction occurs. The asexual reproduction is by cell division and the sexual reproduction involves the formation of zygospores. The gametes migrate from the parental cells, passing through pores to fuse in a region midway between the parental walls. The zygote can form a very ornate wall. This specimen was collected in a moor located in the Salzburger Land, Austria. This images emphasizes the mid-cell of Cosmarium venustum. The isthmus has a slight aperture. Each semi-cell contains one pyrenoid. This specimen measures 38 microns long and 26 microns wide. Differential interference contrast.

Gonatozygon (go-nat-owes-eye-gone) brebissonii. Cells are mostly elongated and cylindrical and slightly bent. The apices are swollen and rounded. The nucleus is located centrally. The cell wall may be covered with dots, granules or short spines. Each semi-cell contains a single, ribbon-like chloroplast with many aligned pyrenoids. The chloroplasts may be slightly spiralled and are centrally placed. Cells can be loosely attached together to form a filament. This genus is found in moderate to weakly alkaline waters (pH 6-6.8) in bog ponds or moors. This specimen was collected in freshwater ponds near Konstanz, Germany. The two separated chloroplasts are visible as is the central located nucleus. 200 microns. Differential interference contrast.

Cosmarium (coz-mare-ee-um) praemorsum is a very common and large genus of phytoplankton alga found usually in oligotrophic, acid waters. The cells of this genus are composed of two semi-cells, constricted in the middle. This region in the middle is called the isthmus and is the site of the nucleus. The outer portions of each semi cell contains a single, large chloroplast. The outer cell wall of each semi-cell are covered with pores and can be very ornate and the appearance can be used to define the species. The cells are move slowly as the result of mucilage secretion. Both asexual and sexual reproduction occurs. The asexual activity is cell division and the sexual reproduction involves the formation of zygospores. The gametes migrate from the parental cell walls through pores and fuse in a region midway between the parental walls. The zygote can form a very ornate wall. Focal plane on the conspicuous ornate of the cell wall. This specimen was collected in a moor located in the Salzburger Land, Austria.

Cosmarium (coz-mare-ee-um) tetraophthalmum is a very common and large genus of phytoplankton alga found usually in oligotrophic, acid waters. The cells of this genus are composed of two semi-cells, constricted in the middle. This region in the middle is called the isthmus and is the site of the nucleus. The outer portions of each semi cell contains a single, large chloroplast. The outer cell wall of each semi-cell are covered with pores and can be very ornate and the appearance can be used to define the species. The cells are move slowly as the result of mucilage secretion. Both asexual and sexual reproduction occurs. The asexual activity is cell division and the sexual reproduction involves the formation of zygospores. The gametes migrate from the parental cell walls through pores and fuse in a region midway between the parental walls. The zygote can form a very ornate wall. This specimen was collected in a moor located in the Salzburger Land, Austria.

Cosmarium (coz-mare-ee-um) tetraophthalmum is a very common and large genus of phytoplankton alga found usually in oligotrophic, acid waters. The cells of this genus are composed of two semi-cells, constricted in the middle. This region in the middle is called the isthmus and is the site of the nucleus. The outer portions of each semi cell contains a single, large chloroplast. The outer cell wall of each semi-cell are covered with pores and can be very ornate and the appearance can be used to define the species. The cells are move slowly as the result of mucilage secretion. Both asexual and sexual reproduction occurs. The asexual activity is cell division and the sexual reproduction involves the formation of zygospores. The gametes migrate from the parental cell walls through pores and fuse in a region midway between the parental walls. The zygote can form a very ornate wall. Focal plane on the cell wall covered with pores and conical granules. This specimen was collected in a moor located in the Salzburger Land, Austria. Differential interference contrast.

Cosmarium tetraophthalmum BREB. in RALFS The cells are 1.5 times longer than wide and trapezoid in shape, the cell terminations are truncated. The cell wall is covered with scattered standing warts. The central cuts are deep and strongly broadened towards the periphery.   Dimension: Length 100 – 120 µm, width 60 – 80 µm Ecology: Very adaptable alga, in medium acidic up to alcaline waters Occurrence: Ubiquitous, often abundant 

Cosmarium tetraophthalmum BREB. in RALFS The cells are 1.5 times longer than wide and trapezoid in shape, the cell terminations are truncated. The cell wall is covered with scattered standing warts. The central cuts are deep and strongly broadened towards the periphery.   Dimension: Length 100 – 120 µm, width 60 – 80 µm Ecology: Very adaptable alga, in medium acidic up to alcaline waters Occurrence: Ubiquitous, often abundant

Closterium costatum.

Euastrum agalma.

Euastrum pecten.

Staurastrum aculeatum.