KEY TO PHYLA 17 



IV. PHYLUM PLATHELMINTHES 



1. Free living flatworms with body covered with cilia. CLASS 



TURBELLARIA ~ - 2 



2. Digestive system with three main branches, one toward 

 the head and two running posteriorly ORDER TRICLADIDEA 



V. PHYLUM COELHELMINTHES 



1. (4) Worms with cylindrical bodies, not segmented. Cov- 

 ered with cuticula. CLASS NEMATHELMINTHES 2 



2. (3) A longitudinal lateral line on each side of body. 

 Body usually tapering at one end _ ORDER NEMATODA 



3. (2) Without lateral line. Adults live in water, larvae are 

 parasitic in insects. Body practically uniform diameter through- 

 out _ ORDER GORDIACEA 



4. (i) Body segmented, without jointed appendages. CLASS 



ANN ELIDA 5 



5. (6) Body with anterior and posterior suckers. Nearly al- 

 ways without setae SUB-CLASS HIRUDI N EI 



6. (5) Setae present and regularly distributed around each 

 segment SUB-CLASS CHAETOPODA, ORDER OLIGOCHAETAE 



VI. PHYLUM MOLLUSCA 



1. (2) Body without a distinct head, usually bilaterally sym- 

 metrical. Bivalve shell. Mantle bilobed CLASS ACEPHALA 



2. ( i ) Molluscs with body always asymmetrical, frequently 

 spiral. Shell in one piece ~ CLASS GASTEROPODA 



VII. PHYLUM ARTHROPODA 



i. (44) Head provided with a single pair of jointed anten- 

 nae in addition to any feeler-like organs which are attached im- 

 mediately around the mouth opening 2 



2 - (3) Without distinctly jointed appendages on the thorax, 

 often with non-jointed appendages. Entirely legless or with 

 abdominal prolegs. Head frequently reduced and retracted with- 

 in the pointed apex of the thorax 



...CLASS INSECTA, ORDER DIPTERA (larvae) 



3. (2) Thorax bearing jointed legs ... 4 



