But Tenebrae was a he and dog-like so..it would certainly help if Centurions didn't classify their genders to start with in the first place -.- Aqua called herself a she and she's certainly feminine while Tenebrae calls himself a he and...
Okay, again, my animal anatomy maniac rears its ugly side X3; either mythical or not
The Centurions (as well as the Summoning Spirits, as proved by their altering appearances in other Tales games) shape themselves as what they want to look like. But even with Aqua's features, she's just trying to look human, but - okay, can't believe I'm saying this - but they're just "blank" features...like a Barbie doll.
They're just energy in a physical form, basically, but they're all...anthros, essentially. Things in a humanlike form.
Except for Volt from Symphonia, but he was different xD (though he DOES have humanlike eyes)