PLANKTONIC FORAMINIFERAL ECOLOGY and PALEOECOLOGY
Published:August 01, 1980
The oxygen isotopic composition of Globigerinoides sacculifer in 30 surface sediment samples from the southwestern Indian Ocean has been measured. The coverage is sufficient to enable isotherms to be constructed from isotopically estimated temperatures, which reflect the effect of the Agulhas Current. The isotopic measurements indicate near summer temperatures. Isotopic analysis of samples from the 18,000 B.P. level in cores should permit paleo-isotherms to be constructed for the Agulhas Current of the glacial period.
Globigerinids display a wide variety of pseudopodial types during their existence in cultures. Development of many long, flexible axopodia from reticulopodia extended into the water above the test allows newly collected specimens recovering on a substrate to float free. With time, the numerous axopodia present in young globigerinids are replaced by fewer brittle, calcifying spines, each coated with a motile cytoplasmic film which extends beyond the spine tip as a sticky, retractable “probe.” Resorption of spines enables mature globigerinids to assume a benthic existence in cultures, moving and feeding with filopodia, reticulopodia, and pharopodia. Globigerinids are rivaled only by acantharians in the diversity of motile appendages which appear in cultured specimens. Radiolarians and heliozoans have much simpler pseudopodial arrays. Globigerinid axopodia are superficially similar to those of heliozoans, but apparently lack the ability to contract rapidly which is essential to food capture in some heliozoans. The greater firmness and length of globigerinid axopodia and young spines allows continuous utilization of detrital food while helping to support flotation of the relatively heavy test.