274 Animal Biology 



In a general survey of the animal kingdom each phylum of animals 

 will be considered from the following standpoints: general character- 

 istics of the phylum and classification of each phylum into classes or other 

 subdivisions. 



Phylum 1. Protozoa (pro to -zo' a) (Gr. protos, first; zoon, animal) 

 General Characteristics 



Most Protozoa are microscopic although a few are visible to the naked eye, 

 some forms being two-thirds of an inch long. All Protozoa are animals, each of 

 which is composed of a single cell (unicellular). This makes them the most sim- 

 ply constructed of all animals. Protozoa exhibit most of the activities which char- 

 acterize the higher, multicellular animals although in a simpler manner. Certain 

 types of Protozoa are colonial ; that is, a number of individuals of one species may 

 be more or less associated in the form of a colony. All Protozoa are complete 

 animals but are without true tissues and organs. Structures similar to true organs 

 of higher animals or which perform functions comparable to organs of higher 

 types are known as organelles. Protozoa were first discovered by Leeuwenhoek, 

 a Dutch naturalist (1632-1723). Many types of Protozoa are parasitic, thus 

 living in or on the bodies of living plants or other living animals. Under such 

 conditions they sometimes produce disease and thus are known as pathogenic 

 Protozoa. For a more detailed discussion consult the chapter on economic im- 

 portance of animals, and the chapter on unicellular, microscopic animals. Number 

 of species of Protozoa, 15,000. 



Classification of the Phylum Protozoa 



Class 1 — Sarcodina (sar ko -di' na) (Gr. sarx, protoplasm or f^esh). — These 

 unicellular animals possess protoplasmic pseudopodia ("false feet"). 



Subclass A — Rhizopoda (ri-zop'oda) (Gr. rhiza, root; pous, appendage 

 or foot). — These Protozoa "creep" by means of pseudopodia of one kind or an- 

 other. 



Examples: Amoeba proteus (Figs. 75, 157, and 159), Endamoeba histolytica 

 (Fig. 264), and various other amoeboid types (Fig. 75). 



Subclass B — Actinopoda (ak ti -nop' od a) (Gr. aktin, ray; pous, ap- 

 pendage). — These amoeboid Protozoa are spherical, floating forms with radiat- 

 ing, raylike, unbranched pseudopodia. 



Examples: Actinophrys (Fig. 75) and Thalassicola (Fig. 75). 



Class 2 — Mastigophora (mas ti -gof o ra) (Gr. mastix, whip; phoreo, to 

 bear) or Flagellata (flaj el -la' ta) (L. flagellatus, whip). — These Protozoa travel 

 by means of one or more whiplike flagella, and are commonly called flagellates. 



Subclass A — Phytomastigina (fi to mas ti -ji' na) (Gr. phyton, plant; mas- 

 tigion, whip or flagellum). — These flagellated Protozoa somewhat resemble plants. 

 Colored bodies known as chromatophores (kro' ma to fors) (Gr. chroma, color; 

 phoreo, to bear) are usually present. 



Examples: Euglena (Figs. 76 and 173), Phacus (Fig. 76), Trachelmonas 

 (Fig. 76), Paranema (Fig. 76), Volvox (Figs. 174 and 175), Chlamydomonas 



