Biocalcification in porcelaneous foraminifera.

Area of Science:

• Biomineralization
• Marine Biology
• Geochemistry

Background:

• Foraminifera are significant marine calcifiers contributing to global carbon cycles.
• They were thought to use distinct biomineralization pathways: extracellular matrix mineralization (rotaliids) and intracellular vesicle mineralization (miliolids).

Purpose of the Study:

• To investigate and compare biomineralization pathways in Foraminifera, specifically porcelaneous miliolid shells.
• To challenge the established dichotomy of Foraminifera calcification models.

Main Methods:

• High-resolution scanning electron microscopy (SEM) was used to examine porcelaneous miliolid shells.
• Analysis focused on the precipitation and structure of high-Mg calcite mesocrystals.

Main Results:

• High-Mg calcitic mesocrystals in porcelaneous shells precipitate *in situ*, forming a dense meshwork.
• Evidence suggests calcified needles do not pre-precipitate within transported vesicles, contradicting the intracellular vesicle model.
• Mesocrystalline chamber walls likely form via intravesicular accumulation of an amorphous mineral phase, crystallized within the extracellular matrix.

Conclusions:

• Foraminifera likely utilize less divergent calcification pathways than previously assumed.
• Biomineralization in Foraminifera aligns with recent principles of controlled crystallization within privileged extracellular spaces.
• These conserved pathways evolved independently in the Paleozoic era.