(Reason for out-of-sequencing: to express, in the light of this story, the sentiment that GW can kiss my authorial ass, too. Along with everyone else who has ever used the term, whose earliest usage that I am aware of dates to the 1920s. Come sue me, melonfarmers.)
Space Marine: Yep. Except, as we said back in [will in the future say in] Space is an Ocean, they’re just regular legionaries who happen to be assigned to ships, habs, drifts, etc. in space, so in practice, the entire ground-based military of the Empire are Space Marines, or at least one assignment order away from it. (When so much of your territory is, well, space, why would you even bother training troops that can’t operate in it?)
And, yes, they all wear some kind of Powered Armor, but the heavy legionaries play this to the max with their walking-tank-style combat exoskeletons.