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breathing, digestion, excretion, growth, reproduction. 

 Most Protozoa are unicellular. 



A multicellular animal is one in which the body is com- 

 posed of many cells, differentiated and grouped to form 

 layers or special tissues with distinct functions. This 

 specialisation for particular function is physiological division 

 of labour. All animals, except Protozoa, are multicellular 

 (Metazoa) when fully developed. 



Explain the Terms Symbiosis and Commensalism. 



Symbiosis meins "living together for mutual benefit." 

 It is an intimate association of two organisms interde- 

 pendent for discharge of vital functions (e.g., Radiolarians 

 and " Yellow Cells:'} 



Commensalism means " eating at the same table." It 

 is a partnership beneficial to both, but of a less intimale 

 nature than symbiosis (e.g., Sea-Anemone and Hermit 

 Crab), 



What is meant by the Term Invertebrate? 



It is a collective name used to distinguish all animals 

 which do not belong to the Phylum Vertebrata. It signi- 

 fies " backboneless " Invertebrates have no internal 

 supporting notochord or backbone. In the Invertebrata 

 the main nervous system is typically ventral, the eyes 

 (when present) are skin-derived, and the heart (when 

 present) is dorsal. 



PHYLUM PROTOZOA. 



What are Protozoa ? 



Organisms in which the individual or body consists of 

 a single cell or a colony of independent cells which are not 

 differentiated into layers or tissues. 



Certain Protozoa show structural complexity, but many 

 are of the simplest morphological type. 



