By Eldon C. Muehling
Historically, the term protozoa were regarded as the counterpart or partner group of bacteria but the term is no longer used in modern taxonomy, according to Wikipedia and other sources. The term is still used informally in High School education today and for purposes of this article, I will describe protozoa as a diverse group of mostly unicellular and mobile organisms with mostly animal-like characteristics.
Protozoa are well-known for their diversity and the fact that they have evolved under so many different conditions. They are usually non-green but some protozoa do contain chlorophyll and are capable of making their own food supplies!
Water is a basic requirement for all protozoa. Thus they are all restricted to aquatic habitats. In spite of this limitation, they are very widespread. They may be found in oceans, seas, lakes, rivers…even stagnant ponds of
freshwater as well as soil and decaying plant or animal matter.
While many protozoan species are solitary organisms, some live in colonies. Even though some protozoa are free-living, others form symbiotic relationships with other life forms. Some species are actually predators of certain species of bacteria.
Others feed by engulfing small particles of plant or animal matter. To assist with capturing prey, many protozoans have developed an ability to move and also to protect themselves from the environment by forming cysts around themselves. Unfortunately chlorine does not usually kill them!
Naturally we are the most concerned about those that are disease-causing parasites of plants and animals and especially humans. A few examples of diseases caused by human protozoan parasites are as follows:
- Sleeping Sickness
- Primary Amoebic Meningoencephalitis
- Trichomonas vaginalis
- And many others
Wikipedia estimated that there are an estimated 30,000 protozoan species but Enclopedia.Com placed the number at more than 50,000! At any rate, suffice it to say that they are very numerous and they can be found all around us.
Fossilized specimens of protozoa have been discovered that are visible to the naked eye, measuring 20 mm (.78 inch) in diameter, but the vast majority of protozoa found today are microscopic. Many of them measure less than 1/200 mm. A few freshwater species are up to 3 mm in length. This is large enough to be visible. In spite of their diminutive size, many of them form complex and fascinating shapes…a beauty which is usually overlooked. We are much more concerned about avoiding water that contains these water-borne contaminants. How fortunate we are that distillation will destroy and remove them from our drinking water virtually 100%. Thank you Pure Water!