208 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 9 



Unicellular 

 Multicellular 



Radially or bilaterally symmetrical 

 No definite organs nor body form 

 With definite organs and body form 

 Quadrilaterally symmetrical, with a head end 

 No vascular, respiratory or skeletal system 

 Without a special food collecting mechanism 

 Flattened 

 Cylindrical 

 With a special ciliated food collecting apparatus 

 With a vascular system and a respiratory system 

 No true skeleton 

 Unsegmented 

 Segmented 

 With a skeleton 

 Without gill clefts 

 Skeleton soft 

 Skeleton hard 



Unsegmented externally 



With a tentacular food collecting mechanism 

 Without a special food collecting mechanism 

 Segmented externally 

 With gill clefts 

 Nerves ventral 



With a tentacular food collecting mechanism 

 Without a special food collecting mechanism 

 Nerves Dorsal 



No definite head, and a special food collecting mechanism 

 Food collecting apparatus internal 

 Food collecting apparatus tentacular and external 

 With a definite head 



