Diversity Of Soil Organisms – Part 8

 

Protists Continued…

Excavata

Morphology
The general body-type in this very diverse group is a small cell with a cilium directed backwards that generates locomotion and directs food (mostly bacteria) toward a feeding groove on the ventral surface, as observed in Fornicata. Many groups prefer low oxygen or anaerobic environments. In contrast to many Excavata groups, the Kinetoplastea (commonly called kinetoplastids) have a characteristic mitochondrion with a large amount of DNA and rely on dissolved nutrients for food (they are osmotrophic). In Parabasalia, the single body-type is replicated hundreds of times to form large multiciliated cells. Both Parabasalia and Preaxostyla have elaborate supporting cytoskeletal elements that provide shape and assist in locomotion. The Heterolobosea are generally amoeboid species with two or four cilia that are used to move in search of food, but some have lost either the ciliated stage or the amoeboid stage. The Euglenids are typically spindle-shaped cells covered by a flexible pellicle; and they can be photosynthetic or not, with the non-photosynthetic species feeding on bacteria or other protists.

Taxonomy
The Excavata is a supergroup, with genera that occur in soil included in six phyla: Fornicata, Parabasalia, Preaxostyla, Discoba, Heterolobosea and Euglenozoa.

Microhabitat
Heterolobosea are found in every ecosystem but are rarely the dominant protists, except in some disturbed soils. The Euglenida, both photosynthetic and heterotrophic genera, occur in soils that are regularly moist or water-saturated (e.g. in wet soil and in riparian areas). Among the Discoba, some free-living species occur in the order Jakobida, such as those of the genus Andalucia. Diversity, abundance and biomass There are approximately 562 described species of Parabasalia and Preaxostyla, more than 80 species of Heterolobosea and more than 1,520 species of Euglenozoa.

Other protists
Nuclearia, Ancyromonas and others (Some Images below)
There are several genera that belong to the base of the Opisthokonta, the group that includes animals and fungi. These genera are common in soil, though rarely abundant, and contribute to the ingestion of bacteria. These include Nuclearia, Fonticula, and the Rozella. Several genera found in soils cannot yet be placed into our classification system. They are placed as incertae sedis in the eukaryotes. These include Ancyromonas, Breviata and Apusomonadida.

Ref: Global Soil Biodiversity Atlas p39