Chapter 21 

 Order 5 Foraminifera d'Orbigny 



THE Foraminifera are comparatively large Protozoa, living al- 

 most exclusively in the sea. They were very abundant in geo- 

 logic times and the fossil forms are important in applied geology 

 (p. 10). The majority live on ocean bottom, moving about slug- 

 gishly over the mud and ooze by means of their pseudopodia. Some 

 are attached to various objects on the ocean floor, while others are 

 pelagic. 



The cytoplasm is ordinarily not differentiated into the two zones 

 and streams out through the apertures, and in perforated forms 

 through the numerous pores, of the shell, forming rhizopodia which 

 are fine and often very long and which anastomose with one another 

 to present a characteristic appearance (Fig. 5). The streaming move- 

 ment of the cytoplasm in the pseudopodia are quite striking; the 

 granules move toward the end of a pseudopodium and stream back 

 along its periphery. The body cytoplasm is often loaded with brown 

 granules which are apparently waste matter and in some forms such 

 as Peneroplis pertusus these masses are extruded from the body 

 from time to time, especially prior to the formation of a new cham- 

 ber. Contractile vacuoles are usually not found in the Foraminifera. 



The test of the Foraminifera varies greatly in form and structure. 

 It may show various colorations — orange, red, brown, etc. The ma- 

 jority measure less than one millimeter, although larger forms may 

 frequently reach several millimeters. The test may be siliceous or 

 calcareous and in some forms, various foreign materials, such as 

 sand-grains, sponge-spicules, etc. which are more or less abundantly 

 found where these organisms live, are loosely or compactly cemented 

 together by pseudochitinous or gelatinous substances. Certain forms 

 show a specific tendency in the selection of foreign materials for the 

 test (p. 47). Siliceous tests are comparatively rare, being found 

 in some species of Miliolidae inhabiting either the brackish water or 

 deep sea. Calcareous tests are sometimes imperforated, but even in 

 such cases those of the young are always perforated. By far the ma- 

 jority of the Foraminifera possess perforated calcareous tests. The 

 thickness of the shell varies considerably, as do also the size and 

 number of apertures, among different species. Frequently the per- 

 forations are very small in the young and later become large and 

 coarse, while in others the reverse may be the case. 



The form of the shell varies greatly. In some there is only one 

 chamber composed of a central body and radiating arms which repre- 



493 



