Pore Structures in Planktonic Foraminifera

Résumé du livre

Pores in shells of planktonic foraminifera are tubular openings created by resorption of previously deposited calcite at fixed sites of the chamber walls. Near the proximal end of each pore, the confluence of outer and inner organic layers on both sides of the primary organic membrane (POM) produces a pore plate. In spinose species, the inner organic lining (IOL) is in contact with the pore plate. The latter is penetrated by a field of micropores (~0.1 micrometer diameter), which may allow the intake and excretion of soluble or colloidal material. Although fine rhizopodial strands do protrude through the micropores, it is unlikely that pores provide direct communication between external rhizopodia and intrashell cytoplasm. In non-spinose species belonging to the genera Globorotalia, Globoquadrina, and Pulleniatina, the proximal organic layers form a thick imperforate IOL that is spatially separated from the pore plate and prevents cytoplasmic communication through the pore. One major difference between spinose and non-spinose species is that the pores in the former group may serve in metabolic exchange and excretion, whereas this function is either absent or reduced in the non-spinose species, in which the IOL is believed to act as a protective and impervious "lining" for the cytoplasm.