Protozoa are a diverse group of single-celled organisms, with more than 50,000 different types represented. The vast majority are microscopic, many measuring less than 1/200 mm, but some, such as the freshwater Spirostomun, may reach 0.17 in (3 mm) in...

Single celled animals which reproduce by binary fission. The majority metabolize solid organic food and are aerobic. These organisms are classified in five groups. (1) Sarcodina. Included is the pathogen Entamoeba histolytica. (2) Mastigophora. These...

Simple single-celled organisms that, unlike bacteria (see BACTERIUM), contain a nucleus. Many are capable of movement; indeed, some are highly mobile within their own environment, possessing short threads (cilia) or long threads (flagella) extending...

Protozoa are a very varied group of single-celled organisms, with more than 50,000 different types represented. The vast majority are microscopic, many measuring less than 1/200 mm, but some, such as the freshwater Spirostomun, may reach 0.17 in (3 mm)...

Protozoa (in Greek proto = first and zoa = animals) are one-celled eukaryotes. That implies that protozoa are unicellular microbes whose cells have membrane-bound nuclei that commonly show characteristics usually associated with animals -- mobility and...

A worldwide scientific effort to catalog every living species has topped the 1 million milestone.Six years into the program the total has reached 1,009,000, researchers report. They hope to complete the listing by 2011, reaching an expected total of about 1.75 million species.Thomas M. Orrell,...