Protozoa, in the classical sense, are single-celled microscopic animals which are heterotrophic (consumers rather than producers capable of manufacturing their own food) and which move by pseudopods (like amoebas), flagella (like Giardia of beaver fever infamy), or cilia (like Paramecium). An important feature of these organisms is that they are composed of only one kind of cell. However, since scientists have carried out cladistic analysis, Protozoa are no longer recognized as a taxon.
Some important organisms formerly called protozoans include foraminifera which are amoeboid types which build distinctive shells of organic material, sand or calcium carbonate. They keep building new rooms in these shells and growing into new accommodation as well as staying in the old space too. Some shells become visible to the naked eye. Deposits of foram shells are often used to establish the relative order in which sedimentary rocks were deposited in the past. ‘Globigerina ooze’ covers vast areas of ocean floor with the calcareous shells of Globigerina and other foram taxa. Radiolarians are other amoeboid type cells with elaborate skeletons made of silica. These accumulate on the sea floor too. Forams and radiolarians often are found as very large cells, occasionally several mm in diameter.
With the advent of the new evolutionary classification schemes, organisms that were formerly classified together with recognizable names have now assumed new identities. Today the whole system is in chaos with strange groupings and unfamiliar names. The new domain name is Protista and all the eukaryotes are included under its umbrella!
An article from international specialists reflected on the problem of classification: “How did we get into this mess?” Their answer was: “The purpose of classification is to arrange biological diversity in such a way as to facilitate communication and accurate information retrieval. This system must operate within a phylogenetic context and must be able to accommodate modification while retaining name stability.” They further declare: “The mess that arose in the classification of protists attest to the failure of the ICBN and ICZN to arrive at mutually satisfactory accommodation, at accommodating changes in the classification, and providing unambiguous name stability in a modern evolutionary context.” [Sina M. Adl et al. 2007. Diversity, Nomenclature, and Taxonomy of Protists. Systematic Biology 56 #4 pp. 684-689 see p. 686.] Perhaps this stability is an impossible task! The problem could be the evolutionary assumptions underlying all these revisions.
The placement of the former protozoons in the new classification is approximately as follows (underlined names are former protozoans):
(Un-named category) Unikonta (organisms with no motile cells or with a single posterior flagellum) – includes phylum Sarcomastigophora including Giardia (beaver fever) and Phylum Amoebozoa including naked amoebas and phylum Opisthokonta which includes aquatic fungus chytrids which are killing frogs worldwide, all true fungi and all many celled animals.
(Un-named category) Bikonta (organisms with two or more flagella which are not situated in posterior location in the cell) – includes Kingdom Archaeoplastida of green algae and land plants; next kingdom Chromista includes infrakingdom Rhizaria with foraminifera and radiolarians; another infrakingdom with brown algae, red algae, diatoms, many aquatic fungi; another infrakingdom with ciliates (like Paramecium), also another group contains Plasmodium which causes Malaria. There are also other groups like algal dinoflagellates. You can see that the single celled former protozoans are now scattered throughout the totality of the eukaryotic world. No wonder classification and identification of all eukaryotic organisms is in chaos!
The new classification schemes try to reflect constantly changing views on evolutionary lines of descent. These schemes are chaotic since groups formerly clustered together are now scattered all over the taxonomic map. In that these new schemes lack the logical consistency of former categories based on form and function, it is proving very hard to figure out what features go with any given taxon. As evolution is a false concept, there is no underlying reality for these schemes to reflect, so the chaos will likely continue indefinitely.