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"Oceanographers have known about these diatom-cyanobacteria symbioses in waters around Hawaii for many years," said Christopher Schvarcz, lead author of the study, "but the species we discovered are something quite different."
The new diatom species are smaller and belong to a different lineage with an elongated, or "pennate" shape with bilateral symmetry. Their symbionts are also smaller and unicellular, and they do not glow under fluorescent light because they do not contain chlorophyll, making them nearly invisible inside the diatom.
That likely explains why they went undetected for so long. The scientists discovered the new species by adding samples of seawater to nitrogen-poor growth medium in the lab, then carefully examining the cultures under a microscope over a period of weeks to months to see what phytoplankton would grow.
https://www.nsf.gov/discoveries/disc_su ... _id=304662