Practical Course in Zoology: Study Guide - T. A. Dauda 2014

Protozoa

General characteristics

More than 30,000 species of this subregnum are known. Morphologically, protozoans consist of a single Cell, yet physiologically they function as independent organisms. Both uninucleate (monoenergid) and multinucleate (polyenergid) forms are distinguished. In terms of Organization, the latter approach Multicellular Organisms. Furthermore, colonial forms are quite common among protozoans. Thus, the term "protozoa" encompasses organisms representing various Levels of biological organization. The body size of protozoans is predominantly microscopic. The smallest are parasitic flagellates and piroplasms, measuring 2–4 µm across. Average sizes range from 50 to 150 µm (0.05–0.15 mm). Some protozoan species reach 1.5 mm and even up to 10 mm in length.

The vast majority of protozoans inhabit aquatic environments and damp soils; additionally, numerous species have adapted to parasitic life within the Organs, Tissues, and Cells of various invertebrate and vertebrate animals. The unicellular body of a protozoan, much like any cell in a multicellular Organism, consists of Cytoplasm and one or more nuclei. However, in multicellular organisms, each individual cell represents only a part of the whole, specialized to perform a specific function (such as epithelial, Muscle, nerve, or secretory cells). Conversely, the single cell forming the body of a protozoan constitutes an autonomous organism exhibiting all fundamental manifestations of life: Nutrition, growth, locomotion, irritability, reproduction, and Respiration. To carry out these Functions, the protozoan cytoplasm contains specialized differentiated structures analogous to the organs of Multicellular animals, known as Organelles or organoids. For instance, a protozoan's body possesses organoids for feeding, movement, and so forth. Despite being unicellular, a protozoan achieves such a high degree of Structural and functional complexity that comparing it to an individual cell of a multicellular animal is difficult, leading some to describe protozoans as non-cellular in Structure. Some protozoan species form colonies comprising large numbers of individuals.

This subregnum of unicellular organisms comprises 5 phyla, though only 3 of these will be examined in this study guide.

1. Sarcomastigophorans (Sarcomastigophora) are protozoans whose locomotor organelles are either transient cytoplasmic projections known as pseudopodia or whip-like extensions called flagella. The phylum Sarcomastigophora is divided into two classes: Sarcodina and Mastigophora.

2. Ciliates, or Infusorians (Ciliophora). Their organelles of locomotion consist of numerous cilia. Ciliates represent the most complexly structured protozoans.

3. Sporozoans (Sporozoa). All representatives of this phylum are parasitic, and throughout their life cycle, they typically form spores that serve for species dissemination.