SIMPLE LIFE 



131 



both salt and fresh waters feature a diversity of 

 species; however large organisms appear definitely 

 reduced in individuals and species. Some species 

 even grow upon glacial ice and others upon mud to 

 almost dry soil. 



Some species grow within or upon other organisms. 

 A few occur in man's intestinal tract. Some occur 

 upon the shells of turtles or aquatic arthropods. 

 Others may be found upon and provide color to the 

 hair of arboreal mammals, especially sloths. Certain 

 unicellular forms are within and occasionally may 

 parasitize protozoans, sponges, and coelenterates. 

 Some can be found upon or within plant leaves and 

 roots. 



The blue-green algae are of economic importance. 

 Perhaps their only benefits exist in the food and 

 oxygen they provide other organisms and in the 

 source of biological information they provide to 

 biologists and naturalists. Unfortunately, their 

 primary relationship with man is detrimental. The 

 various floating species form sticky scums that cover 

 many bodies of fresh water. Such scums contribute 

 to noxious odors and disagreeable tastes in water 

 supplies. When abundant, the decaying individuals 

 may produce poisons and deplete oxygen to the point 

 of killing fish and other aquatic organisms. Even 

 livestock and water fowl may die if they drink 

 water containing the poisons. 



PROTISTA 



With the dawn of the Actualistic Phase of geologi- 

 cal history, the scene was set for the evolution of more 

 modern types of organisms. Probably both the 

 protozoan and fungi subkingdoms of protistans were 

 derived from the monerans. Perhaps the origin of 

 protistans was very rapid. The first protistans prob- 

 ably were photosynthetic flagellates (ancestral 

 protozoans) and archaic representatives of the true 

 fungi. However, where and from what did they origi- 

 nate? There can be little doubt that the ocean was 

 the site of protistan origin. Also, it is believed that 

 either the protistans had a single moneran ancestor, 

 or the flagellates evolved from the early blue-green 

 algae and the fungi from the early bacteria. Only 

 assuming a single origin of protistans from monerans 

 would satisfy the common ancestor requirement for 

 a Kingdom Protista. Although this possibility is fol- 

 lowed in the scheme of classification, it appears more 

 likely that the protozoans and fungi originated in- 

 dependently. Belief in separate origins is based on 

 observation of present Monera and Protista and on 

 a very scanty, almost useless fossil record. For such 

 a double origin of protistans two moneran groups 

 must, over a great period of time, have developed a 

 well-organized nucleus and other features to make 

 the transition from protoplasmic to unicellular or- 

 ganization. Actually the two similar but independent 

 transitions would not have had to be great. The first 

 two groups of protistans could have been little more 

 than strange, archaic, blue-green algae (ancestral 

 flagellate protozoans) and bacteria (ancestral fungi), 

 and evolution from there on would have been a rela- 



tively simple matter. Therefore, although admitting 

 the likelihood of two protistan ancestors, we retain 

 our classification for convenience in emphasizing lev- 

 els of organization. 



PROTISTA AS PLANTS OR ANIMALS 



In the taxonomic classification of most botanists 

 and zoologists, the phyla here assigned to the King- 

 dom Protista are considered members of the plant or 

 animal kingdoms, rather than being classified sepa- 

 rately. That solution is possible and satisfactory for 

 many taxa. The protistans Sarcodina, Sporozoa, and 

 Ciliophora are in most classifications treated as 

 animals, members of the animal phylum Protozoa. 

 They lack chlorophyll, and so are unlikely to be 

 confused with plants. The true fungi (Eumycophyta) 

 can be considered members of the plant kingdom. 

 However, some of the Flagellata (those bearing 

 chlorophyll) and all of the slime molds (Myxomyco- 

 phyta)can be classified as either plants or animals. 

 Today many botanists distribute the confusing 

 flagellates throughout many phyla of algae and the 

 slime molds in a single [)hylum allied to the fungi; 

 zoologists, on the other hand, place both groups in 

 the Phylum Protozoa, the green flagellates as a 

 subclass of a Class Flagellata and the slime molds as 

 a group of the Class Sarcodina. 



As mentioned earlier, the protistans and monerans, 

 except for differences in basic organization, might be 

 classified as a single kingdom. .Some taxonomists 



