User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-76.69.7.125-20111215193456/@comment-76.69.7.125-20111215200203

Its title seems to be "Deep Sea King" or "Deep Sea Dragon", something like that. That's a pretty reasonable explanation for why a subspecies would exist. Doesn't mean it's real just yet.

If Tigrex ever shows up, I expect him to have a Rare Species so there could be a All Cover Monsters Rare Species event quest.