It's still an Infernal Arm, not an oceanic one. Aspects don't change its nature, just some of its flavor.

[More green light erupts from his hand, winding across the battlefield and seeking out another set of foes to strike. As the shades erupt back into their ghastly forms, Zagreus is ready and waiting with a swing to cut them down.]

Is it a secret, then? Or are you just shy about it?