portrait

Description:

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).