PHYLUM PROTOZOA 



39 



b. Rhizopoda in General 



The Protozoa which are included in the class Rhizopoda 

 have been grouped into four principal orders according to the 

 character of their pseudopodia and the structure of their shells, 

 if these are present: (i) Lobosa, (2) Heliozoa, (3) Radio- 



LARIA, (4) FORAMINIFERA. 



Order i. Lobosa. Rhizopoda with fingerlike (lobose) pseudo- 

 podia. Most of the Lobosa occur in fresh water, a few in 

 moist earth, and some are parasites. 

 Examples: Ameba (Fig. 9), Arcella / 



(Fig. 16), and Difflugia (Fig. 17). 



Arcella (Fig. 16) is common in the 



Fig. 16. — Arcella discoides (order 

 Lobosa) as seen from above, 7, shell; 

 2, pseudopodia ; 3, edge of opening 

 into shell; 4, thread attaching animal 

 to interior of shell; 5, nucleus; 6, food 

 vacuole ; 7, gas vacuole. (From 

 Leidy.) 



Fig. 17. — Difflugia urceo- 

 lata (order Lobosa) as seen 

 from the side. 1, shell com- 

 posed of minute particles of 

 sand; 2, pseudopodia. (From 

 Leidy.) 



ooze on the bottoms of fresh-water ponds and ditches. It has 

 a dome-shaped brownish shell of chitin (/) which it secretes. 

 The lobose pseudopodia (2) protrude from a circular opening (j) 

 in the center of the flattened surface. 



Difflugia (Fig. 17) is another common member of the order 

 Lobosa, and is also found in the ooze of ponds. Its shell (/) 

 consists of minute particles of sand and other foreign objects 

 held together by chitin. 



