The coral symbionts are reclassified into a family of genera

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A systematic revision splits what had been treated as the single genus Symbiodinium, informally divided into clades A to I, into a family, Symbiodiniaceae, containing several genera — among them Cladocopium and the heat-tolerant Durusdinium. The revision matters beyond nomenclature: the lineages are separated by an evolutionary distance comparable to that between families of other organisms, so treating "zooxanthellae" as one interchangeable partner had been obscuring the very differences in thermal tolerance that determine whether a coral bleaches.

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