Shell-Material Variation in the Agglutinated Foraminifer Trochammina Pacifica Cushman

Abstract

Test construction, reproduction, and rate of growth in specimens of Trochammina pacifica cultured without mineral grains are analogous to those of specimens supplied with sediment. Newly formed test chambers consist of fragile, organic membranes. Control specimens show selectivity for grain size but not for mineral composition. The median grain size of disaggregated control specimens agreed closely with the median grain size of the supplied sediment. The grain size in a test, however, increases gradually as individuals become larger during ontogenetic development. These findings are applicable to taxonomic analyses and to the paleoecological interpretation of fluctuating, shallow-water, marine environments and their depositional history.