SIMPLE LIFE 



137 



Reproduction: asexual budding and conjugation are 

 common; encystment regularly takes place and is 

 related to an unfavorable period; an asexual life cycle 

 appears most typical. 



Occurrence: regularly found in the ocean and in 

 fresh water, generally upon living or nonliving ob- 

 jects; some are parasitic. 



The ciliated, free-living, young suctorians resemble 

 ciliates. After swimming for a while the young lose 

 their cilia and change into an attached adult stage. 

 The adults usually are attached to objects by a 

 contractile stalk. 



SUBKINGDOM FUNGI 



In the two phyla here considered, the slime molds 

 (or slime fungi) constitute the Phylum Myxomyco- 

 phyta and the true fungi (including the algal fungi, 

 sac fungi, and club fungi) constitute the Phylum 

 Eumycophyta. Also treated here are the lichens. 



The limits and relationships of most protists are 

 a subject of much controversy, the consequences of 

 an already mentioned poor fossil record. The con- 

 troversy extends to the present groups. Some biolo- 

 gists believe that the slime molds, true fungi, and 

 even the bacteria represent subphyla of a single 

 phylum, hence had a common ancestor. At the other 

 extreme are biologists who would segregate the 

 slime molds, each of the three true fungi classes, and 

 the bacteria into individual phyla. The present inter- 

 pretation of relationships, then, assumes a common 

 ancestor for all fungi. 



Division of the Subkingdom Fungi into two phyla 

 shows where common ancestry is less likely to be 

 present. There is good evidence that slime molds 

 are unrelated to true fungi; slime molds may have 

 evolved from the Sarcodina and true fungi from the 

 Flagellata. Under the present interpretation it is 

 assumed that the evidence for single origin of a Sub- 

 kingdom Fungi from the earliest Protista is true. In 

 the case of the true fungi, there are apparent fossils 

 from the dawn of Actualistic times, almost two billion 

 years ago. 



The Subkingdom Fungi includes the majority of 

 plant-like creatures that do not contain chlorophyll 

 and do not belong to the Kingdom Plantae. Only the 

 bacteria share this plant-like nature and lack of true 

 chlorophyll. For this and other reasons, bacteria 



sometimes are classified as fungi. However, fungi 

 possess single-cell or more complex organization and 

 have their basic structure in the form of hair-like 

 filaments called mycelia. 



Diagnosis: organization unicellular to simple 

 cellular; nucleus diflferentiated, complete and com- 

 plex; generally plant-like, most possess definite cell 

 walls and are nonmotile; chlorophyll absent; struc- 

 ture usually hair-like (filamentous); cell division 

 regularly by mitosis or meiosis, amitosis less 

 common. 



MYXOMYCOPHYTA (Slime Molds 

 or Slime Fungi) 



The slime molds are truly remarkable creatures. 

 For much of their life cycle they are very much like 

 flagellates (Figure 8.8). A motile, flagellate swarm 

 cell is released from a spore. These swarm cells (or 

 swarm spores) move about by means of their flagellae 

 and engulf food by surrounding it with protoplasmic 

 projections of their cell body. The swarm cells then 

 become more spherical in shape and lose their flag- 

 ella, becoming Sarcodina-like myxamoebae. These 

 myxamoebae divide mitotically to provide gametes. 

 Gametic fusion and zygote formation start the de- 

 velopment of a multinucleate protoplasmic mass, or 

 Plasmodium. The plasmodium might still be con- 

 sidered animal-like because it is slow moving. How- 

 ever, the Plasmodium soon becomes nonmotile and 





sporangia 

 sclerotium * 



spores 



swarm spores 



Figure 8.8 Life cycle of a typical slime mold. 



