252 The Sarcodina 



arise mainly from an ectoplasmic stalk (raphe, peduncle) which extends 

 through the aperture (Fig. 5. 43, G). In types with perforate tests, most 

 of the pseudopodia may arise from the ectoplasm enclosing the test. 



The pseudopodial pattern varies to some extent with environmental 

 conditions, and in at least certain species (Fig. 5. 35, D-F), may undergo 

 marked changes during development of the young organism. Although 

 myxopodia are often characterized as pseudopodia showing a more fluid 

 outer layer and a less fluid core, it is sometimes impossible to distinguish 

 the two zones. However, even the more delicate myxopodia may show a 

 certain degree of stiffness, in that they tend to follow a straight line and 

 often extend unsupported for considerable distances through the water. 

 The pseudopodia of certain species (Fig. 5. 44) sometimes assigned to 

 the order apparently are filopodia. 



The Foraminiferida are markedly holozoic. The pseudopodial net 

 traps other Protozoa, algae (especially diatoms), and sometimes larval 

 Crustacea and other small invertebrates. The captured food is proinptly 

 surrounded by cytoplasm. Food is usually drawn toward the test by a 

 shortening of appropriate pseudopodia, and such particles may move at 

 the rate of several millimeters an hour. Unless size is prohibitive, the 

 prey may be drawn inside the test; diatoms, in particular, are often 

 found in the endoplasm. However, the myxopodial net itself may have 

 marked digestive abilities, although variation is noted from species to 

 species. In general, the shorter myxopodia show greater digestive activity 

 than the long delicate pseudopodia (82). Digestion often begins soon after 

 the food is surrounded by cytoplasm and may be completed before the 

 material reaches the test. In such types as Elphidium crispwn this seems 

 to be the normal method, to the exclusion of digestion within the endo- 

 plasm (66). 



Other pseudopodial activities include the construction of tests and 

 cyst walls. Such activities are especially noticeable in species which build 

 arenaceous tests and cysts. In multilocular types, the addition of a new 

 chamber to the test is often carried out within an arenaceous cyst wall 

 laid down by the pseudopodia outside the area of the new chamber (Fig. 

 5. 35, A-C). Within the cyst, the pseudopodia form a reticulum outlining 

 the cavity of the new chamber and the new wall is developed at the 

 surface of the mass. If materials for a cover are excluded from cultures, 

 formation of a new chamber proceeds without encystment in Elphidium 

 crispum (66). 



Many Foraminiferida are motile. Their characteristic creeping depends 

 upon the contraction of distally attached pseudopodia, the body being 

 dragged along the substratum as a result. Although creeping species may 

 seem restless under laboratory conditions and can travel several milli- 

 meters in an hour, such locomotion is relatively sIoav in terms of size of 

 the organism. 



