Braarudosphaera bigelowii

Braarudosphaera bigelowii is a coastal coccolithophore in the fossil record going back 100 million years to the Late Cretaceous.

Coccolithophore
The family Braarudosphaeraceae consist of single-celled coastal phytoplanktonic algae with calcareous scales with five-fold symmetry, called pentaliths. With 12 sides, it has a regular dodecahedral structure, approximately 10 micrometers across.



Nitroplast


B. bigelowii has a nitroplast organelle, originated some 100 million years ago from a cyanobacterial endosymbiont called UCYN-A2, which allows B. bigelowii to fix nitrogen and convert it into compounds useful for cell growth. This phenomenon is previously known from diatoms in the family Rhopalodiaceae, where a nitrogen fixing and non-photosynthetic cyanobacterial endosymbiont, a diazoplast, provides the photosynthetic host cell with nitrogen.

Name
The genus name Braarudosphaera is in honour of Norwegian botanist Trygve Braarud (1903–1985). He specialized in marine biology, and was affiliated with the University of Oslo.