Test ultrastructure and taphonomy of the monothalamous agglutinated foraminifer Cribrothalammina, n. gen., alba (Heron-Allen and Earland)

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Abstract
Cribrothalammina n. gen. alba (Heron-Allen and Earland) is a finely agglutinated foraminifer with a flexible and resilient test in living individuals. The test consists of an inner organic lining and agglutinate (quartz grains, clay, diatom frustules) embedded in an organic cement; a single aperature was observed in all specimens. Staining with ruthenium red in TEM preparations permitted the visualization of acid mucopolysaccharides in both the organic cement and the inner organic lining. In the cement, acid mucopolysaccharides appear as numerous fine strands that bind individual grains of agglutinate, whereas those of the inner organic lining fornm a fine-grained lineation parallel to the plasmalemma. The test undergoes major alterations duriung gametogenesis. Ten to 15 prominent pores form that penetrate the test wall. They appear in a fairly regular array over the test surface and serve as the sole avenue for gamete release. This unusual feature, in addition to other aspects of the test, necessitate a taxonomic change, namely the description of a new genus, Cribrothalammina. When gamete release is completed, the test collapses and soon disaggregates. Ultrathin sections of such tests reveal the presence of numerous bacteria within the outer portions of the test wall, which appear to degrade the organic components of the test. Although modern C. alba is widely distributed geographically, it has no known fossil record.

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