User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-1712810-20121221133256

So, I asked about the Pelagus changed to Fanged Beast thing... and here's the very official answer I got:

"If the Pelagus monsters ever come back to the series, they'll most likely be reclassified as Fanged Beasts since they're the same classification as Arzuros in Japanese. Don't take my word for it though! It's just speculation at this point.

The reason for the change is because while doing research for monster names during Ultimate we realized something about the Pelagus classification and sought to make it better rather than just sticking to old legacy terms simply because they were commonly known." - Andrew, Localization Project Director/Manager