Braarudosphaera bigelowii

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

Braarudosphaera bigelowii Temporal range: Late Cretaceous–present PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
(unranked):	Haptophyta
Class:	Prymnesiophyceae
Order:	Coccosphaerales
Family:	Braarudosphaeraceae
Genus:	Braarudosphaera
Species:	B. bigelowii
Binomial name
Braarudosphaera bigelowii (Gran & Braarud) Deflandre[1]

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.^[2][3]

(A) SEM image of a cell of B. bigelowii surrounded by 12 pentaliths. A pentalith (calcareous scale of the Braarudosphaeraceae) indicated by the blue open pentagon consists of five trapezoidal segments. Black arrow indicates "side length of the pentalith" where the measurements were conducted. (B) SEM image of pentalith of B. bigelowii (proximal side). (C) Close up of proximal side in previous image showing laminar structure. (D) – (F) light microscope images of three different specimens.^[2]

Nitroplast

A nitroplast inside B. bigelowii (coccoliths removed), marked by a black arrow. Like other haptophytes, the cell has 2 unequal flagella.

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.^[4][5][6] 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.^[7][8]

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.^[9]