We have to create a scientific name for a virus that infects a particular alga: Phaeocystis globosa. The name 'phaeocystis globosa' is a feminine noun and an adjective.
So, how to translate "virus of Phaeocystis globosa" into Latin: "virus phaeocyst[?] globosae", what would be the declension of "Phaeocystis" in genitive?
UPDATE
Due to rarity of species epithets formed from full host names, the adjective will be dropped.
Phaeocystis sounds like a combination of Greek φαιός (phaiós, "gray" or "harsh") and κύστις (kýstis, "bladder"). So the Greek genitive would be Phaeocysteos (Φαιοκύστεως).
But in biology, my understanding is that it's standard to use Latin forms even when the names come from Greek words. And in Latin, cystis would be a third-declension noun, so the genitive would also be cystis.
In other words, the Latin genitive would be Phaeocystis globosae: "of the round gray-sack".
