The word protista came from Greek meaning the very first; they are eukaryotic in nature. Eukaryotes are a group of organisms with nucleus under the domain: eukarya while the kingdom consists of both multicellular and unicellular organisms, these organisms were not plants, animals or fungi and as a result do not fit into any other kingdom. Therefore, the term protista has been adopted to refer to organisms that appear similar but are not from the same group (taxon). The word Protista has now been abandoned and focus has been shifted to the various lineage that exists within it.
General Characteristics of Kingdom Protista
1. Many are unicellular while some are multicellular.
2. They are eukaryotes.
3. Some are motile while some are non-motile.
4. They move either by flagella, cilia or may be ameboid in nature.
5. Some are heterotrophic in nature (including the parasitic forms); while some are photosynthetic, others may be both photosynthetic and heterotrophic (mixotrophic).
6. They are mostly aquatic, some are found in moist soil while others live in the body of plant and animals.
7. Their mode of reproduction can be either by asexual or sexual means: binary fission and conjugation.
Phyla
There are controversies among scientists concerning some classification of certain organisms into phylum as the name protista is not monophyletic i.e organisms having the same ancestral origin. For instance, the older phylum protozoa consists of animal-like organisms that may not be from the same ancestral origin (clade); also classification of some algae into kingdom plantae or protista is also controversial. However, there are about 16 phyla in the kingdom protista grouped into five informal groups based on mobility and nutrition namely;
1. Heterotrophs (no locomotor apparatus): This group include Rhizopoda, Actinopoda and Foraminifera.
2. Photosynthetic (protists): This include pyrrophyta, euglenophyta, chrysophyta, Xanthophyta, Bacillariophyta, Rhodophyta, Phaecophyta and chlorophyta.
3. Heterotrophs (with flagella): Sarcomastigophora, Ciliophora.
4. Non-Motile (spore formers): Apicomplexa
5. Heterotrophs (with restricted mobility): Oomycota, Acrasiomycota and Myxomycota.
Rhizopoda e.g Amoebas (move by pseudopodia). They were formerly classified as protozoa.
Actinopoda e.g Radiolarians having glassy-like skeletons with needle-like pseudopodia.
Foraminifera e.g Forams having shells and moving by protoplasmic streaming.
Pyrrophyta e.g Dinoflagellates which are regarded as Red tides are photosynthetic (having chlorophyll a and b), and possessing two unequal flagella.
Euglenophyta e.g Euglena which possess flagella, possess chloroplast containing chlorophyll a and b; they are photosynthetic.
Chrysophyta Include e.g Golden Algae (chrysophyceae); also include diatoms (bacillariophyceae) and yellow-green algae (Xanthophyceae)
Rhodophyta e.g Red Algae which are mostly multicellular, containing red pigment and chlorophyll a.
Phaecophyta e.g Brown Algae such as Kelps are multicellular, contain chlorophyll a and c.
Chlorophyta include Green Algae such as Chlamydomonas are also multicellular; contain chlorophyll a and b.
Sarcomastigophora e.g Trypanosome (Zoomastigotes) are multicellular animal-like organisms containing flagellum and are parasitic; transmitted by vectors Tsetsefly (Glossina palpalis and Glossina moritans). They were formerly classified as phylum protozoa.
Ciliophora e.g Paramecium are multicellular animal-like organisms having cilia and are free living. They were formerly classified as protozoa.
Apicomplexa e.g Plasmodium (formerly classified as protozoa) are multicellular animali-like organisms that are non motile, spore formers (sporozoans) and parasitic.
Oomycota e.g Water molds, rusts and mildews which are both terestial and freshwater organisms.
Acrasiomycota e.g cellular slime molds such as Dictyostelium which are in colony of cells and are similar to amoebas.
Myxomycota e.g plasmodial slime molds such as Fuligo which stream along with multinucleated mass of cytoplasm.
It is important to note that the Kingdom Protista and some phyla such as Protozoa have been abandoned. Scientists have come up with the new classification system that do not include kingdoms rather, consist of supergroups.
