wet lenses/domes

[Antonio]

Hello to everyone in the board,
reading here and there i found people mentioning wet lenses with domes. Are they referring to a wet lens mounted onto a housing dome port (is it even possible to do?) or to a dedicated dome port mounted on the lens itself? what would be the point? i thought that wet lenses were already designed to take care of the optical problems underwater.
And, since we are at it, wet lenses are always an add on to a lens already in the housing, i.e. never been produced body only in the housing with separated wet lenses outside, am i correct?