SIMPLE LIFE 



133 



of primary concern here. However, it shows that a 

 seemingly simple thing such as structural type is not 

 agreed upon in a group of creatures that are quite 

 numerous and are studied a great deal. No matter 

 what view makes the most sense to you, if you wish to 

 be correct, refer to the protozoans as orgamsmal rather 

 than as either unicellular or acellular. You could be 

 even more descriptive by calling these creatures 

 "organismal, cell-like protists." 



FLAGELLATA ( = MASTIGOPHORA) 

 (Flagellates) 



Diagnosis: characterized by one or more whip- 

 like flagellae that provide a typical locomotion; 

 flagellae present during one to all stages of the life 

 cycle; individual's shape mostly fixed — oval, spheri- 

 cal, or elongate; shape maintained either by a firm ex- 

 ternal pellicle that normally is ridged spirally or 

 longitudinally, or by armor, plates, cases or shells; 

 those species without firm body coverings change 

 shape by a flowing of their cytoplasm (pseudopodia 

 allowing amoeboid movement) and if they lack 

 flagellae these protistans resemble the Sarcodina; 

 occur as individuals or colonies, colonial forms 

 branching or held together by a jelly-like material or 

 cellulose; may be motile or nonmotile, nonmotile 

 species generally attached by a stalk or enclosed by 

 a jelly-like mass (Figure 8.3). 



Structure: individuals distinct or without cell mem- 

 branes or cell walls, so nuclei are in a continuous 

 cytoplasm; nucleus complete and complex, one to 

 many per individual, but no nucleus is especially 

 larger than any others (see Ciliophora); cytoplasmic 

 pigments when present include green chlorophyll in 

 plastids, but the green is sometimes masked by a 

 dense red in the cytoplasm; possible organelles (com- 

 plex structures) include flagellae, plastids, vacuoles, 

 an eyespot or stigma, trichocysts, and various rods 

 and fibers of unknown function; flagellae usually one 

 or two, also more or none during certain stages of the 

 life cycle; flagellae are the principal source of loco- 

 motion and food gathering, or of food capture by en- 

 tangling; locomotion also may involve a worm-like 

 movement; plastids, when present, are variously 

 shaped and constitute the site of photosynthesis; con- 

 tractile vacuoles, generally two, rarely more, are near 

 flagellae bases; contractile vacuoles commonly 

 present in fresh-water species, absent elsewhere, 

 function in excess water removal; contractile 



FLAGELLATES 



Euglena 



Pandonna 



Astasia 



Monosiga 



Trypanosoma 



Ceratium 



Figure 8.3 Flagellate types, all microscopic. 



vacuoles without contributing canals or vacuoles as 

 in ciliates; nonflagellate species often have a large 

 central vacuole; stigma, a red spot that is light sensi- 

 tive, is typically associated with a gullet that contains 

 the basal part of a flagellum; trichocysts (mostly 

 ciliate organelles) may be discharged as long threads 

 that may be used to attach, to capture food, or to de- 

 fend against predators. 



Nutrition: photosynthetic, chemosynthetic, or 

 holozoic. 



Reproduction: mostly asexual by binary fission; 

 also asexual by fragmentation and multiple fission; 

 some are sexual and display either diplobiontic or 

 one of the haplobiontic life cycles; in many species 

 the life cycle is complex. 



