About pleiad.. as you know, Pleiades - is 1) 7 daughters from the Greek mythology, 2) a star cluster/constellation. But wikipedia (see 'Alexandrian_Pleiad') states that: "In modern times, "pleiad" is also used as a collective noun for a small group of brilliant or eminent persons." I'm not sure if I ever met this usage in English, but that's how the word is normally used in Russian, often accompanied by 'whole'. The author knows about this usage, and he sees that the word is somehow related to the constellation's name. So he generalized it to 'a bunch'. Maybe he wasn't perfectly correct here, but it happens in Russian as well.