442 Annals New York Academy of Sciences 



in the literature and suggests a whole spectrum of ecological factors that may 

 have been involved. 



In both modern tropical and subtropical waters, spindle-shaped tests seem 

 to characterize definite depth zones (20 to 80 meters). By extrapolation, 

 Bandy^^ ascribed equivalent depth zones to fusulinids — an extinct Paleozoic 

 family — and to the Cretaceous spindle-shaped Loftusia. Similarly, he noted 

 that deeper water assemblages seem to show a size increase and coarser surface 

 features. 



The planktonic foraminifers show a variety of morphological and structural 

 adaptations for their floating existence.^^ The variations are ascribed to 

 temperature and saUnity. Thin walled shells, for example, characterize surface 

 Orbulina miiversa and Globigerina in contrast to thick walled shells for indi- 

 viduals living at greater depths. Reduction in the specific gravity of the 

 planktonic test is also affected by increase in pore size, aperture enlargement, 

 or the development of supplementary apertures. 



Resistance to sinking which is the critical problem facing all pelagic protist 

 inhabitants, is attained in planktonic foraminifers as follows: flattening of the 

 body accompanied by a radial test, and elongate or clavate chambers. In the 

 Orbulinidae and Hantkennidae spinose projections develop. Other adaptations 

 include: globose chambers that increase in size as added, large primary aper- 

 tures, and in such forms as Globigerinoides, development of many secondary 

 openings. 



Although all of the above named variations may be related to genetical 

 events and the operation of natural selection, there are other nongenetical 

 factors known to influence foraminiferal morphology. On the Argentine shelf, 

 a depauperate foraminiferal fauna was found to be characterized by its small 

 size, partial or complete loss of ornamentation, a tendency toward asym- 

 metry, and growth retardation. Spectrographical study of trace elements in 

 the shells revealed the presence of lead in depauperate, as compared to, normal 

 faunas in which it was absent.^^ ■'*^ Study of Allogromia laticoUaris in culture 

 revealed occasional populations with a large number of flattened discoidal 

 individuals. In this instance, the flattening was directly attributed to "down- 

 ward pressure exerted by rapidly multiplying algal filaments."'*^ Dwarfed 

 foraminifers are reported from poorly ventilated basins.^- 



An unusual example of a testate protozoan, Difflugia oblonga, can be cited 

 here although it belongs to a different order than the foraminifers. A small 

 pond (10 X 6 meters) in the environs of Prague, Czechoslovakia, contained 

 numerous individuals of this species. They exhibited an astonishing morpho- 

 logical variation. Every variant was observed from a globose bowl with a 

 smooth base, to elongate figures with tapered basal projections variously 

 curved. Some specimens took on the configuration of an Erlenmeyer flask 

 with knoblike projections from each basal edge. The heavy discharge of 

 industrial waste gas (CO2) in the environs was thought to be the causative 

 factor .^^ 



Classes Chrysophyceae, Coccolithophorida, and Silicoflagellata 



The several flagellates cited in the subtitle of this section, with the diatoms 

 discussed earlier, constitute the phylum Chrysophyta. Members of the order 



