User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-76.69.7.125-20111215193456/@comment-3062343-20111215200825

The title listed on the Japanese wiki is 冥海竜, which translates to "Dark Sea Wyvern", since regular Lagiacrus is just 海竜, I think we'll be seeing a black/dark blue Lagiacrus relatively soon.